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Aluksi mielenkiintoinen tutkimusartikkeli "Is calorie a calorie a calorie?" tiivistelmänä ja otteita jutun tekstiosasta. Lukekaa etenkin luvut:
METABOLIZABLE ENERGY, ENERGY EXPENDITURE, IS A CALORIE A CALORIE? ja CONCLUSION
Lisäksi muutamia muita tutkimusartikkeleja (abstraktit/PubMed):
Weight-loss with low or high carbohydrate diet?
A randomized trial of a low-carbohydrate diet for obesity.
The Effects of Low-Carbohydrate versus Conventional Weight Loss Diets in Severely Obese Adults: One-Year Follow-up of a Randomized Trial
*Tässä linkki * Full-text tai PDF*
A Randomized Trial Comparing a Very Low Carbohydrate Diet and a Calorie-Restricted Low Fat Diet on Body Weight and Cardiovascular Risk Factors in Healthy Women
Mukavia lukuhetkiä!
Is a calorie a calorie?
Buchholz AC, Schoeller DA.
Department of Nutritional Sciences, University of Wisconsin-Madison, 1415 Linden Drive, Madison, WI 53706, USA.
Am J Clin Nutr. 2004 May;79(5):899S-906S.
The aim of this review was to evaluate data regarding potential thermodynamic mechanisms for increased rates of weight loss in subjects consuming diets high in protein and/or low in carbohydrate. Studies that compared weight loss and energy expenditure in adults consuming diets high in protein and/or low in carbohydrate with those in adults consuming diets low in fat were reviewed. In addition, studies that measured the metabolizable energy of proteins, fats, and carbohydrates were reviewed. Diets high in protein and/or low in carbohydrate produced an approximately equal to 2.5-kg greater weight loss after 12 wk of treatment. Neither macronutrient-specific differences in the availability of dietary energy nor changes in energy expenditure could explain these differences in weight loss. Thermodynamics dictate that a calorie is a calorie regardless of the macronutrient composition of the diet. Further research on differences in the composition of weight loss and on the influence of satiety on compliance with energy-restricted diets is needed to explain the observed increase in weight loss with diets high in protein and/or low in carbohydrate.
Publication Types:
· Review
· Review, Tutorial
PMID: 15113737 [PubMed - indexed for MEDLINE]
http://tinyurl.com/3ntx9
Täydennyksenä tekstiosat alkuperäisestä:
ABSTRACT
The aim of this review was to evaluate data regarding potential thermodynamic mechanisms for increased rates of weight loss in subjects consuming diets high in protein and/or low in carbohydrate. Studies that compared weight loss and energy expenditure in adults consuming diets high in protein and/or low in carbohydrate with those in adults consuming diets low in fat were reviewed. In addition, studies that measured the metabolizable energy of proteins, fats, and carbohydrates were reviewed. Diets high in protein and/or low in carbohydrate produced an 2.5-kg greater weight loss after 12 wk of treatment. Neither macronutrient-specific differences in the availability of dietary energy nor changes in energy expenditure could explain these differences in weight loss. Thermodynamics dictate that a calorie is a calorie regardless of the macronutrient composition of the diet. Further research on differences in the composition of weight loss and on the influence of satiety on compliance with energy-restricted diets is needed to explain the observed increase in weight loss with diets high in protein and/or low in carbohydrate.
Key Words: Weight loss • energy metabolism • protein • Atkins diet
INTRODUCTION
High-protein diets, low-carbohydrate diets, and combined high-protein and low-carbohydrate diets have been highly popularized, and this is particularly true of the Atkins diet (1). This is not an entirely new phenomenon because both the high-protein diet and the protein-sparing modified fast have been popular in the not-too-distant past (2–9). As a consequence of this more recent interest, however, several controlled trials were performed to test the efficacy of these diets (10–18). Despite the initial skepticism of many investigators, these recent studies found that high-protein and/or low-carbohydrate diets do yield greater weight losses after 3-6 mo of treatment than do low-fat diets (10–13).
We identified 9 studies of free-living adults in which weight losses in subjects consuming diets high in protein and/or low in carbohydrate were compared with those in subjects consuming diets high in carbohydrate and/or low in fat (Table 1). Of these studies, 6 lasted 12 wk. On average, consumption of the high-protein and/or low-carbohydrate diets resulted in 12-wk and 24-wk weight losses that were 2.5 ± 1.8 ( ± SD) and 4.0 ± 0.4 kg greater, respectively, than those that resulted from consumption of the high-carbohydrate and/or low-fat control diets. If these weight losses are assumed to have the typical composition of 80% fat and 20% fat-free mass (19), then this difference in weight can be estimated to reflect a 19 500–31 300-kcal difference in energy balance, or 186–233 kcal/d. These findings, however, are enigmatic because the energy intakes of the treatment groups in most studies were similar. This has caused several investigators to ask whether a calorie is indeed a calorie or whether a calorie is dependent on the macronutrient composition of the diet. We herein review the possible explanations for this difference in energy balance.
THERMODYNAMICS
A calorie, by its simplest definition, is a unit of energy and is equivalent to 4.184 absolute J. In the popular press and in the labeling of food products in the United States, a food calorie actually refers to a kilocalorie, or 1000 cal. That is, 1 food cal equals 1 kcal, or the amount of energy needed to raise 1 kg water from 15 to 16 °C.
From a thermodynamic viewpoint, a calorie is of course a calorie. The first law of thermodynamics states that energy can be neither created nor destroyed, but only transformed. Thus, the human body is constantly transforming energy—in this case, kilocalories—by combusting foodstuffs to produce heat. Although this concept is widely held today, our knowledge of life as a combustion process is limited to the last 2–3 centuries and arose from a very old and fundamental question. Because humans and animals are warm and animal heat is the essence of being alive, that question, as variously phrased, was, What is the innate fire, the vital force, animal heat (20)? The Greek philosophers Plato, Aristotle, and Hippocrates and the Roman physician Galen thought that the innate fire was in the heart and that it was somehow related to food, but the scientific answer to this question arose, in part, only in the latter half of the 18th century from the work of Lavoisier in France (21, 22). Lavoisier’s experiments involved the first-ever animal calorimeter, a device used to measure heat production. The outer shell of the calorimeter was packed with snow, which melted to maintain a constant temperature of 0 °C around an inner shell filled with ice. In the core of the inner shell was a wire cage housing a guinea pig. As the ice melted from the heat produced by the guinea pig, the water flowed out of the calorimeter and was collected and weighed. Each kilogram of melted ice water represented 80 kcal heat given off by the animal. Lavoisier noted that, in 10 h, the guinea pig melted 0.37 kg ice, thus producing 29.6 kcal heat (0.37 kg x 80 kcal heat/kg). He concluded, "la respiration est donc une combustion." That is, respiratory gas exchange is a combustion, like that of a candle burning.
Across the English Channel, Crawford was also conducting experiments on the heat of combustion in animals. Crawford noted that a given portion of pure air is "altered" by the respiration of an animal and that the extent of this alteration is nearly equal to that produced by combustion of an amount of wax or charcoal that used the same volume of oxygen during combustion. That is, the amount of heat produced per unit of oxygen consumed is nearly the same for animal catabolism as it is for the combustion of inanimate material (23). Lavoisier further concluded that a flame and an animal both consume oxygen, which combines with organic substance to release water and carbon dioxide. Thus, Lavoisier and Crawford showed that from a purely thermodynamic point of view, a calorie is indeed a calorie.
METABOLIZABLE ENERGY
The human body, however, is not a perfect engine, and thus the thermodynamics may not be so pure. It is now known that the energy liberated from the combustion of a food is not identical to the energy available to the body from consumption of that food. This is the concept of "metabolizable energy," or the difference between the gross energy (as measured by bomb calorimetry) of consumed food and the energy contained in feces and urine (also measured by bomb calorimetry) (24). The systematic investigation of the gross energy content of food and of the availability of that energy can be credited to Rubner in Germany and to Atwater in the United States. Both scientists’ work is described in detail by Widdowson (25). Using a bomb calorimeter, Rubner measured the heats of combustion of many different proteins, fats, and carbohydrates found in individual foods. He thus determined the energy density of dietary fat to be 9.3 kcal/g on the basis of the mean combustion values for olive oil (9.384 kcal/g), animal fat (9.372 kcal/g), and butterfat (9.179 kcal/g). The energy density of dietary carbohydrate (specifically of starch and sugar in a mixed diet) was determined to be 4.1 kcal/g on the basis of the average combustion values for glucose (3.692 kcal/g), lactose (3.877 kcal/g), sucrose (3.959 kcal/g), and starch (4.116 kcal/g), which were weighted for their average contribution to a mixed diet. Rubner, however, made no allowance for fecal losses in deriving his calorie-conversion factors for fat and carbohydrate. He did, however, conclude that the heat of combustion of protein in a bomb calorimeter is higher than the energy value available to the host because the body oxidizes protein only to urea, creatinine, uric acid, and other nitrogenous end products, which can themselves be further oxidized in a bomb calorimeter. From urinary and fecal combustion in one subject, Rubner determined that the loss of energy from the nitrogenous substances in urine and feces totaled 23% of energy intake, 16.3% from meat sources and 6.9% from vegetable sources. Thus, meat and vegetable protein differed in their metabolizable energy densities: the former provided 4.23 kcal/g and the latter provided 4.30 kcal/g (after correction for the heat of combustion of nitrogenous end products in urine and losses of nitrogen in feces). Assuming that 60% of dietary protein was from animal sources and 40% from vegetable sources and recognizing that the energy content of wheat and rye protein ("the most important sources of vegetable protein") was overestimated by 7.9% because of the higher nitrogen content in wheat and rye protein than in animal protein, Rubner suggested that 4.1 kcal/g be used as an average factor for determining the energy content of dietary protein. Thus, Rubner showed that a calorie is a calorie; however, he also showed that the human body cannot extract all the calories liberated from combustion of a food and that macronutrients differ according to their chemical composition in the number of calories per unit of weight.
With Bryant, Atwater extended Rubner’s work by studying the availability of the other macronutrients. Data from human digestion experiments were combined with other data in the literature to devise "coefficients of availability" (defined as intake minus fecal excretion divided by intake) for protein, fat, and carbohydrate. Atwater and Bryant applied these coefficients of availability to the heat of combustion of "mixed" diets that were typical of the time (consisting of foods such as beef, butter, ginger snaps, parched cereal, rye bread, baked beans, and canned pears) and were consumed by 3 adult male subjects. The foods consumed, as well as the subjects’ urine and feces, were collected and analyzed for nitrogen and fat content; the difference between total organic matter and the sum of protein and fat was taken to represent carbohydrate. An additional correction was made for protein: for each gram of nitrogen in urine, there was sufficient unoxidized matter to yield an average of 7.9 kcal, or 1.25 kcal/g absorbed protein (7.9 divided by 6.25). Thus, after correction for the coefficient of availability, 1.25 kcal/g was subtracted from the heat of combustion of protein. The calculated availability of the mixed diets agreed closely with the actual availability as found by experiment.
The energy values obtained by Atwater and Bryant’s experiments, to which we refer today as the Atwater factors, are presented in Table 2. The metabolizable energy values in the right column, ie, 4, 9, and 4 kcal/g protein, fat, and carbohydrate, respectively, are more appropriately known as the Atwater general factors for metabolizable energy and were proposed for application to mixed diets of similar composition to those used in Atwater’s experiments. With the use of the Atwater general factors, metabolizable energy is calculated as 4.0P + 9.0F + 4.0TC, where P is protein (P = 6.25 x nitrogen; in g), F is fat (in g), and TC is total carbohydrate (in g, calculated by dry weight difference). Not only have these factors been applied to the total amounts of protein, fat, and carbohydrate in a mixed diet, as Atwater and Bryant had intended, but they have also been used, and continue to be used, in assessing the energy value of individual foods.
At first glance, calculated metabolizable energy would appear to be equivalent to measured metabolizable energy. The work of Atwater and Bryant, however, clearly showed that these factors were average values. Although the general factors could be used to calculate the metabolizable energy of a mixed diet, they were in error to some degree for almost any particular single food item. This error results from differences in chemical structure that can alter the gross energy per unit weight by up to several percent and, to a slightly larger degree, from differences in availability. Thus, although a calorie is still a calorie from a thermodynamic point of view, calculations of the metabolizable energy of a diet that are obtained by using the Atwater general factors are not exact and could thus introduce an error in the calculated metabolizable energy content of a particular food or diet. In recognition of this, a modification of the general factors, the Atwater specific factors, was devised in the mid-1950s for specific classes of foods to account for the differences in the average digestibility of different food groups and thus reduce this potential for error (26).
The Atwater general factors, however, continue to be commonly used. In 1970 Southgate and Durnin (27) tested the Atwater general factors and determined that they were still valid, with one exception. Large amounts of unavailable dietary carbohydrate resulted in increased excretion of fecal fat, nitrogen, and energy, and these findings were subsequently confirmed by other researchers (28–31). Thus, Southgate and Durnin (27) found that the Atwater protein and fat factors overestimate the energy derived from these constituents. Others have since found that the Atwater general factors overestimate the measured metabolizable energy of mixed diets, especially those high in dietary fiber, by a mean (±SD) of 6.7 ± 4.4% (range: 1.2–18.1%) (28–30, 32–35). The reasons hypothesized to explain the effect of dietary fiber on metabolizable energy are many. Dietary fiber may decrease the transit time of food in the intestine (resulting in less time for digestion and absorption), increase bulk and water-holding capacity (reducing the rate of diffusion of digestion products toward the intestinal mucosal surface for absorption), or cause mechanical erosion of the mucosal surface (leading to increased endogenous material) (29, 36). Wisker and Feldheim (28) also note that in contrast with the energy content of protein and fat, the energy content of dietary fiber is liberated by fermentation. Thus, factors affecting the microbial degradation of dietary fiber—the chemical structure of nonstarch polysaccharides, the solubility and degree of lignification of the fiber components, and physiologic factors such as the composition of the colon microflora and the transit time—may affect metabolizable energy (28). This may be the reason why the Atwater general factors were found to overestimate measured metabolizable energy to a greater extent for diets high in nonavailable fiber than for diets high in available fiber (overestimations of 7.0% and 2.6%, respectively; P < 0.05) (35). Together, findings from the above studies show that not all dietary carbohydrates provide 4 kcal/g.
The differences between the general Atwater factors, the specific Atwater factors, and true metabolizable energy might explain some of the difference in weight loss observed after consumption of 2 diets with different fiber content. For example, Miles et al (29) carefully determined the metabolizable energy of 2 diets, one with 16 g fiber and one with 37 g fiber (Table 3). If the energy intakes in this study were extrapolated downward to 2 weight-loss diets each providing 1500 metabolizable kcal/d, one high and the other low in fiber, the Atwater general and specific factors would overestimate the measured metabolizable energy of the high-fiber diet by 120 and 102 kcal, respectively. Similarly, for the low-fiber diet, the Atwater general factors would overestimate metabolizable energy intake by 60 kcal, and the Atwater specific factors by 78 kcal. Thus, if a weight-loss study is performed and the energy intake of the 2 diets is calculated on the basis of the macronutrient content of the diets and the Atwater general factors, the 2 diets would differ in measured metabolizable energy by 60 kcal/d (120 – 60). If one assumes that weight loss averages 80% fat by weight, then this error could account for a difference in weight loss of 0.008 kg/d, or 0.6 kg over 12 wk. If the energy intakes were calculated by using the Atwater specific factors or tabulated food values from the US Department of Agriculture Agriculture Handbook no. 8 (37), which are based on the Atwater specific values, then the 2 diets would differ by 24 kcal/d (102 – 78), and the weight-loss effect would be 0.003 kg/d, or 0.3 kg over 12 wk. This error, however, does not bring into question the thermodynamics of a calorie being a calorie, but it does point to the limits of our ability to determine the exact metabolizable energy intake from a given diet.
ENERGY EXPENDITURE
A second potential mechanism through which diets differing in macronutrient composition can produce differences in energy balance and hence weight loss is a change in energy expenditure. For example, if a particular diet were to increase energy expenditure relative to another diet, then for the same energy intake, energy balance would be more negative for the former diet, and weight loss would probably be greater. Although the most important consideration of energy expenditure with regard to energy balance is total energy expenditure, it is also helpful to look at the components of energy expenditure, ie, resting metabolic rate, the thermic effect of food, and energy expended in physical activity, to understand the mechanism through which macronutrients can alter energy expenditure.
One difficulty in comparing the effects of macronutrients on energy expenditure is the problem of being unable to manipulate only one macronutrient at a time under the experimental restriction of eucaloric feeding. Ten studies of energy expenditure measured in a whole-room calorimeter have been performed; in these studies, protein intake was held constant, and the percentages of energy from fat and carbohydrate were varied (38–47). The fat content of the low-fat diets used in these studies ranged from 3% to 20% of energy, and the fat content of the high-fat diets ranged from 40% to 60% of energy; the protein content was held at 10%, 15%, or 20% of energy. When the protein content was held constant and fat was substituted for carbohydrate, the mean 24-h energy expenditure of the control groups did not differ. Two studies (43, 46) also included a postobese subgroup, in whom 24-h energy expenditure decreased 75–80 kcal/d after consumption of the high-fat diet. When the results of all 10 studies were averaged, the difference in 24-h energy expenditure between the high-carbohydrate and high-fat diets was not different from zero ( ± SD: –19 ± 54 kcal/d).
Resting or sleeping metabolic rates were reported in 7 of these studies (41–47) and were found not to differ between the 2 diets ( ± SD: –21 ± 77 kcal/d). The thermic effect of food was measured in 2 studies (43, 45) and was 58 kcal/d lower with the high-fat diet in one study (45) and tended to be higher with the high-fat diet in the other (43). This topic was also reviewed by Eisenstein et al (48); the average effect of replacing fat (50% of energy) with carbohydrate was 40 kcal/d. Another study was performed in which total energy expenditure was measured by doubly labeled water, and thus the study provided greater freedom for the subjects to expend energy in physical activity (49). This was a crossover study comparing diets in which the protein content was held at 10% of energy, and the carbohydrate content was set at either 7% or 83% of energy. Energy expenditure was measured with doubly labeled water in the free-living participants. Under these conditions, total energy expenditure for the low-carbohydrate diet was 365 kcal/d lower than that for the low-fat diet, but resting metabolic rate and the thermic effect of a meal did not differ significantly between the 2 diets, which indicates that the difference in total energy expenditure was due to a reduction in the energy expended in physical activity.
Although the above studies provide some evidence of a change in the thermic effect of food when fat is substituted for carbohydrate, the magnitude of this change is usually small, and the direction is opposite to the one that would be required to explain a greater weight loss after consumption of a low-carbohydrate diet. This change in the thermic effect of a meal, however, did not translate into a lower total energy expenditure, except when the carbohydrate intake was reduced to a ketogenic level (7% of calories). The reason for this decrease is unknown, but the authors speculated that it was due to reduced physical activity that was secondary to low glycogen stores.
There are fewer studies of the effect of changes in the percentage of energy from protein on total energy expenditure than there are of the effect of changes in total energy intake. The effect of changes in the percentage of dietary energy from protein on the thermic effect of food has been reviewed recently (48). On the basis of a meta-analysis, it was concluded that the thermic effect of food increases 7 kcal/1000 kcal of ingested food for each increase of 10 percentage points in the percentage of energy from protein. Thus, if a subject is instructed to consume a 1500-kcal/d energy-restricted diet with 35% of energy from protein, then the thermic effect of food will be 21 kcal/d higher than if protein contributes only 15% of the dietary energy. Two studies also showed that a high-protein diet is associated with a higher resting metabolic rate. Mikkelsen et al (50) provided participants with a eucaloric diet having 29% or 11% of energy from protein and found that the resting metabolic rate was 51 kcal/d higher with the 29% protein diet. Whitehead et al (47) instructed participants to consume a diet that was energy restricted by 50% and that had either 36% or 15% of energy from protein; the sleeping metabolic rate was 44 kcal/d higher with the high-protein diet. These investigators also measured 24-h energy expenditure by using a room calorimeter and reported that expenditure was 71 kcal/d higher with the high-protein diet (P < 0.05), which was in agreement with the increase in sleeping metabolic rate and the predicted increase in the thermic effect of food.
Thus, although substituting carbohydrate for fat in the diet does not appear to alter total energy expenditure, increasing protein intake to 30–35% of energy does increase energy expenditure. The increase, however, is only 70 kcal/d, or 2.7% of a median 2550-kcal/d total energy expenditure for an adult. If the difference in energy expenditure is assumed to be proportionally reduced with a 1500-kcal/d energy-restricted diet, then the increase in energy expenditure with the higher protein diet would be 41 kcal/d. Given identical energy intake, however, this would increase weight loss by 0.04 kg/wk, or 0.44 kg over a 12-wk course of weight-loss treatment. Note, however, that no measurements have been made by using doubly labeled water in free-living subjects to determine whether changes in energy expenditure from physical activity occur. Inclusion of measures of total energy expenditure in future studies is recommended to provide these data.
IS A CALORIE A CALORIE?
The effects of metabolizable energy and diet-induced changes in energy expenditure indicate that having 2 groups of subjects consume 2 different energy-restricted diets could introduce a different energy imbalance. Should this, however, be considered evidence that a calorie is not a calorie when comparing macronutrients? Dietary intakes calculated by using the Atwater general factors of 4, 9, and 4 kcal/g protein, fat, and carbohydrate, respectively, may be in error with respect to metabolizable energy content. This is particularly true for a high-fiber diet, in which incomplete absorption of the fiber reduces the metabolizable energy provided to the body. This is because the Atwater general factors are not exact constants for calculation of metabolizable energy. Indeed, that is one reason why the food tables from the US Department of Agriculture are calculated by using the Atwater specific factors. As reviewed above, however, even these latter values have been found to overestimate metabolizable energy by 3–7%, particularly when the fiber content of the diet is high. However, this overestimation would lead to a prediction of only a 0.2–0.6-kg weight difference over a 12-wk treatment for a 21-g difference in fiber intake. In addition, diets that are specially formulated from a small number of foods or from isolated proteins, fats, and carbohydrates can also differ in metabolizable energy from the metabolizable energy content calculated by using the Atwater factors because, as stated above, the Atwater factors are average values for a mixed diet, and individual nutrients do deviate from the mean by a few percent. These effects, however, should not be interpreted as a thermodynamic advantage of one diet over another. The difference in energy can be totally explained by the increase in fecal energy, and the reality is that the difference is actually an error in calculating the metabolizable energy of the diets.
Of course, the increased energy expenditure associated with increased protein intake also does not violate the laws of thermodynamics, because the energy is conserved. It does, however, come close to the spirit of the argument that a calorie is not a calorie, because feeding diets that induce a difference in energy expenditure can introduce a difference in energy balance and thus a difference in weight loss. Of the macronutrients, only protein has been found to have this effect, but the magnitude of this effect is small and perhaps accounts for a 0.8-kg difference in weight loss between diet treatments over 12 wk. This difference in predicted weight loss could only account for one-third of the average greater weight loss of 2.5 kg reported for a 12-wk high-protein and/or low-carbohydrate weight-loss diet and thus should not be taken as evidence that a calorie is not a calorie.
CONCLUSION
We conclude that a calorie is a calorie. From a purely thermodynamic point of view, this is clear because the human body or, indeed, any living organism cannot create or destroy energy but can only convert energy from one form to another. In comparing energy balance between dietary treatments, however, it must be remembered that the units of dietary energy are metabolizable energy and not gross energy. This is perhaps unfortunate because metabolizable energy is much more difficult to determine than is gross energy, because the Atwater factors used in calculating metabolizable energy are not exact. As such, our food tables are not perfect, and small errors are associated with their use.
In addition, we concede that the substitution of one macronutrient for another has been shown in some studies to have a statistically significant effect on the expenditure half of the energy balance equation. This has been observed most often for high-protein diets. Evidence indicates, however, that the difference in energy expenditure is small and can potentially account for less than one-third of the differences in weight loss that have been reported between high-protein or low-carbohydrate diets and high-carbohydrate or low-fat diets. As such, a calorie is a calorie. Further research is needed to identify the mechanisms that result in greater weight loss with one diet than with another.
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Weight-loss with low or high carbohydrate diet?
Golay A, Eigenheer C, Morel Y, Kujawski P, Lehmann T, de Tonnac N.
Department of Internal Medicine, University Hospital Geneva.
Int J Obes Relat Metab Disord. 1996 Dec;20(12):1067-72.
OBJECTIVE: With obesity being recognized as an important cardiovascular risk factor, it is important to determine the optimal hypocaloric diet for decreasing that risk. The goal of this study was to compare the effects of two hypocaloric diets of similar caloric value, but differing in carbohydrate content (25% and 45%).
SUBJECTS: Sixty-eight out-patients were followed for 12 w. DESIGN: The patients were assigned to one of two groups that received either a low (25% CHO, n = 31) or a high (45% CHO, n = 37) carbohydrate hypocaloric diet (5.0 MJ/d, 1200 Kcal/d).
RESULTS: After 12 w, the mean weight loss was similar and did not differ significantly between the two groups: 10.2 +/- 0.7 kg (25% CHO) and 8.6 +/- 0.8 kg (45% CHO). Furthermore, loss of adipose tissue was similar, 8.1 +/- 0.5 kg (25% CHO) and 7.1 +/- 0.7 kg (45% CHO). Despite a high protein intake (1.4 g/kg/ideal body weight) there was loss of lean body mass: 2.2 +/- 0.4 kg (25% CHO) and 1.4 +/- 0.3 kg (45% CHO). The waist/hip ratio diminished significantly (P < 0.001) and identically in both groups. The fasting blood glucose (even though normal, along with cholesterol and triglyceride concentrations, were significantly decreased after weight loss. The fasting blood insulin which was mildly elevated before weight loss decreased more markedly with the 25% CHO diet compared to the 45% CHO diet (P < 0.003). The glucose/insulin ratio improved significantly (P < 0.05) after weight loss with both diets (0.17 +/- 0.04 mmol/mU (25% CHO) vs 0.10 +/- 0.03 mmol/mU (45% CHO).
CONCLUSIONS: Neither diet offered a significant advantage when comparing weight loss or other, metabolic parameters over a 12 w period. However, considering the greater improvement of fasting blood insulin, the glucose/insulin ratio and blood triglyceride, the low carbohydrate diet (25%) could be more favourable in the long-term. The improvement of fasting blood insulin could be explained by the differences in monounsaturated fat composition in the low carbohydrate diet.
PMID: 8968851 [PubMed - indexed for MEDLINE]
A randomized trial of a low-carbohydrate diet for obesity.
Foster GD, Wyatt HR, Hill JO, McGuckin BG, Brill C, Mohammed BS, Szapary PO, Rader DJ, Edman JS, Klein S.
The New England Journal of Medicine Volume 348:2082-2090 May 22, 2003 Number 21
University of Pennsylvania School of Medicine, Philadelphia, PA 19104-3309, USA.
BACKGROUND: Despite the popularity of the low-carbohydrate, high-protein, high-fat (Atkins) diet, no randomized, controlled trials have evaluated its efficacy.
METHODS: We conducted a one-year, multicenter, controlled trial involving 63 obese men and women who were randomly assigned to either a low-carbohydrate, high-protein, high-fat diet or a low-calorie, high-carbohydrate, low-fat (conventional) diet. Professional contact was minimal to replicate the approach used by most dieters. RESULTS: Subjects on the low-carbohydrate diet had lost more weight than subjects on the conventional diet at 3 months (mean [+/-SD], -6.8+/-5.0 vs. -2.7+/-3.7 percent of body weight; P=0.001) and 6 months (-7.0+/-6.5 vs. -3.2+/-5.6 percent of body weight, P=0.02), but the difference at 12 months was not significant (-4.4+/-6.7 vs. -2.5+/-6.3 percent of body weight, P=0.26). After three months, no significant differences were found between the groups in total or low-density lipoprotein cholesterol concentrations. The increase in high-density lipoprotein cholesterol concentrations and the decrease in triglyceride concentrations were greater among subjects on the low-carbohydrate diet than among those on the conventional diet throughout most of the study. Both diets significantly decreased diastolic blood pressure and the insulin response to an oral glucose load.
CONCLUSIONS: The low-carbohydrate diet produced a greater weight loss (absolute difference, approximately 4 percent) than did the conventional diet for the first six months, but the differences were not significant at one year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease. Adherence was poor and attrition was high in both groups. Longer and larger studies are required to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets.
Copyright 2003 Massachusetts Medical Society
Publication Types:
· Clinical Trial
· Multicenter Study
· Randomized Controlled Trial
PMID: 12761365 [PubMed - indexed for MEDLINE]
Source Information
From the University of Pennsylvania School of Medicine, Philadelphia (G.D.F., B.G.M., P.O.S., D.J.R.); University of Colorado Health Sciences Center, Denver (H.R.W., J.O.H., C.B.); Washington University School of Medicine, St. Louis (B.S.M., S.K.); and Thomas Jefferson University, Philadelphia (J.S.E.).
Stern, L., Iqbal, N., Seshadri, P., Chicano, K. L., Daily, D. A., McGrory, J., Williams, M., Gracely, E. J., Samaha, F. F. (2004).
The Effects of Low-Carbohydrate versus Conventional Weight Loss Diets in Severely Obese Adults: One-Year Follow-up of a Randomized Trial.
Ann Intern Med 140: 778-785
URL:
http://www.annals.org/cgi/content/full/140/10/778
URL:
http://www.annals.org/cgi/reprint/140/10/778.pdf
The Effects of Low-Carbohydrate versus Conventional Weight Loss Diets in Severely Obese Adults: One-Year Follow-up of a Randomized Trial
Linda Stern, MD; Nayyar Iqbal, MD; Prakash Seshadri, MD; Kathryn L. Chicano, CRNP; Denise A. Daily, RD; Joyce McGrory, CRNP; Monica Williams, BS; Edward J. Gracely, PhD; and Frederick F. Samaha, MD
18 May 2004 | Volume 140 Issue 10 | Pages 778-785
Background: A previous paper reported the 6-month comparison of weight loss and metabolic changes in obese adults randomly assigned to either a low-carbohydrate diet or a conventional weight loss diet.
Objective: To review the 1-year outcomes between these diets.
Design: Randomized trial.
Setting: Philadelphia Veterans Affairs Medical Center.
Participants: 132 obese adults with a body mass index of 35 kg/m2 or greater; 83% had diabetes or the metabolic syndrome.
Intervention: Participants received counseling to either restrict carbohydrate intake to <30 g per day (low-carbohydrate diet) or to restrict caloric intake by 500 calories per day with <30% of calories from fat (conventional diet).
Measurements: Changes in weight, lipid levels, glycemic control, and insulin sensitivity.
Results: By 1 year, mean (±SD) weight change for persons on the low-carbohydrate diet was –5.1 ± 8.7 kg compared with –3.1 ± 8.4 kg for persons on the conventional diet. Differences between groups were not significant (–1.9 kg [95% CI, –4.9 to 1.0 kg]; P = 0.20). For persons on the low-carbohydrate diet, triglyceride levels decreased more (P = 0.044) and high-density lipoprotein cholesterol levels decreased less (P = 0.025). As seen in the small group of persons with diabetes (n = 54) and after adjustment for covariates, hemoglobin A1c levels improved more for persons on the low-carbohydrate diet. These more favorable metabolic responses to a low-carbohydrate diet remained significant after adjustment for weight loss differences. Changes in other lipids or insulin sensitivity did not differ between groups.
Limitations: These findings are limited by a high dropout rate (34%) and by suboptimal dietary adherence of the enrolled persons.
Conclusion: Participants on a low-carbohydrate diet had more favorable overall outcomes at 1 year than did those on a conventional diet. Weight loss was similar between groups, but effects on atherogenic dyslipidemia and glycemic control were still more favorable with a low-carbohydrate diet after adjustment for differences in weight loss.
The Journal of Clinical Endocrinology & Metabolism Vol. 88, No. 4 1617-1623
Copyright © 2003 by The Endocrine Society
A Randomized Trial Comparing a Very Low Carbohydrate Diet and a Calorie-Restricted Low Fat Diet on Body Weight and Cardiovascular Risk Factors in Healthy Women
Bonnie J. Brehm, Randy J. Seeley, Stephen R. Daniels and David A. D’Alessio
University of Cincinnati and Children’s Hospital Medical Center, Cincinnati, Ohio 45221
Address all correspondence and requests for reprints to: Bonnie Brehm, Ph.D., University of Cincinnati, P.O. Box 210038, Cincinnati, Ohio 45221-0038.
Untested alternative weight loss diets, such as very low carbohydrate diets, have unsubstantiated efficacy and the potential to adversely affect cardiovascular risk factors. Therefore, we designed a randomized, controlled trial to determine the effects of a very low carbohydrate diet on body composition and cardiovascular risk factors. Subjects were randomized to 6 months of either an ad libitum very low carbohydrate diet or a calorie-restricted diet with 30% of the calories as fat. Anthropometric and metabolic measures were assessed at baseline, 3 months, and 6 months. Fifty-three healthy, obese female volunteers (mean body mass index, 33.6 ± 0.3 kg/m2) were randomized; 42 (79%) completed the trial. Women on both diets reduced calorie consumption by comparable amounts at 3 and 6 months. The very low carbohydrate diet group lost more weight (8.5 ± 1.0 vs. 3.9 ± 1.0 kg; P < 0.001) and more body fat (4.8 ± 0.67 vs. 2.0 ± 0.75 kg; P < 0.01) than the low fat diet group. Mean levels of blood pressure, lipids, fasting glucose, and insulin were within normal ranges in both groups at baseline. Although all of these parameters improved over the course of the study, there were no differences observed between the two diet groups at 3 or 6 months. ß- Hydroxybutyrate increased significantly in the very low carbohydrate group at 3 months (P = 0.001). Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women.
This work was supported by the American Heart Association, University of Cincinnati Obesity Research Center, University of Cincinnati Research Council, Children’s Hospital Medical Center Clinical Research Center (supported in part by USPHS Grant M01-RR-08084 from the General Clinical Research Center Program, National Center for Research Resources, NIH), and NIH Grants DK-54263 and DK-56863.
Abbreviations: DEXA, Dual energy x-ray absorptiometry; HDL, high density lipoprotein; LDL, low density lipoprotein.
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