Effectiveness of Low-Carb Diet for Weight Loss

These listings are quoted from scientific and medical journals. At then end of each listing, you'll find an expanation in jargon-free English. Every effort was made to keep the explanations true to the original article. However, bear in mind that the explanations were not written by a medical professional, and may contain errors. In a few places, I added my own thoughts. I've tried to mark what's my opinion and what is fact. Let us know if you have any suggestions for improvements or corrections.

Sincerely, Joshua M. Yelon

Loss of weight, sodium and water in obese persons consuming a high- or low-carbohydrate diet.

Rabast U, Vornberger KH, Ehl M
Ann Nutr Metab 1981;25(6):341-349

Isocaloric 5.61 mJ (1,340 kcal) formula diets involving the isocaloric exchange of fat and carbohydrate were fed to 21 obese persons selected for sex, height, and weight before the start of the treatment and distributed over three groups. The weight loss observed during the carbohydrate-restricted diets was significantly greater than during the high-carbohydrate diet. After 28 days of treatment the weight loss recorded on the high-carbohydrate diet was 9.5 +/- 0.7 kg, as compared to 11.4 +/- 0.7 kg (p less than 0.05) on the corn oil-containing diet and 12.5 +/- 0.9 kg (p less than 0.01) on the butter-fat-containing diet. The weight loss achieved was not dependent on the type of fat administered (saturated vs. polyunsaturated). When calculated cumulatively, sodium excretion during the first 7 days was significantly greater on the low-carbohydrate diet, whereas after 28 days the total amount of sodium excreted was highest on the high-carbohydrate diet. Potassium excretion during the low-carbohydrate diets was significantly greater for as long as 14 days, but at the end of the experimental period the observed differences no longer attained statistical significance. At no time did the intake and loss of fluid and the balances calculated therefrom show significant differences. From the findings obtained it appears that the alterations in the water and electrolyte balance observed during the low-carbohydrate diets are reversible phenomena and should thus not be regarded as causal agents of the different weight reduction.

Comments: they got 21 people, gave 7 of them a diet with lots of carbs, 7 a diet with lots of vegetable oil, and 7 a diet with lots of butter. All groups got 1340 calories per day. All groups lost the same amount of water weight. The low-carbers lost 1.25 times as much real weight at the high-carbers. They didn't mention whether that weight loss was muscle or fat.

Effects of aerobic exercise and dietary carbohydrate on energy expenditure and body composition during weight reduction in obese women.

Racette SB, Schoeller DA, Kushner RF, Neil KM, Herling-Iaffaldano K. Department of Medicine, University of Chicago, IL 60637.
Am J Clin Nutr 1995 Mar;61(3):486-494

To test the benefits of aerobic exercise and dietary carbohydrate during reduced-energy feeding, 23 obese women (44 +/- 4% fat) were randomly assigned to either aerobic exercise (Ex) or no exercise (Nx), and to a low-fat (LF) or low-carbohydrate (LC) reducing diet (5.00 +/- 0.56 MJ/d) for 12 wk. Changes in body composition, postabsorptive resting metabolic rate (RMR), thermic effect of a meal (TEM), and total daily energy expenditure (TDEE) were measured by respiratory gas exchange and doubly labeled water. Significant effects of Ex included a greater loss of fat mass (Ex: -8.8 +/- 2.1 vs Nx: -6.1 +/- 2.3 kg, P = 0.008) and maintenance of TDEE (Ex: +0.07 +/- 1.23 vs Nx: -1.46 +/- 1.04 MJ/d, P = 0.004), due to a difference in physical activity (Ex: +0.75 +/- 1.06 vs Nx: -0.61 +/- 1.03 MJ/d, P = 0.006), which was not attributable solely to the Ex sessions. RMR in both groups decreased comparably (-0.54 MJ/d), and TEM (% of meal) did not change. Diet composition did not significantly influence body composition or energy expenditure changes, but a greater weight loss was observed after the LC than after the LF (-10.6 +/- 2.0 vs -8.1 +/- 3.0 kg, P = 0.037) diet. The addition of aerobic exercise to a low-energy diet was beneficial in the treatment of moderate obesity because of its favorable effects on body composition, physical activity, and TDEE.

Comments: They got 23 women, and split them into two groups: a low-carb group, and a high-carb group. They don't mention here how low-carb the low-carb diet was, or how many calories they ate. They dieted for 3 months. In both groups, body composition (relative amounts of fat, muscle, and water) was unchanged. The low-carb group lost 1.3 times as much weight.

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):1067-1072

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.

Comments: 68 people were split into two groups: half received a low-carb diet, the other received a high-carb diet. Notice that the low-carb diet wasn't very low, and the high-carb diet wasn't very high. So, the difference between the diets is very small. They stayed on the diet for 3 months. Both groups lost fat, the low-carbers lost 1.14 times as much. Both groups lost "lean body mass", a lump term meaning water, glycogen, muscle, and everything else other than fat. The low-carbers lost 1.57 times as much lean body mass (not surprising --- we know that low-carb causes some water loss).

Weight loss with high and low carbohydrate 1200 kcal diets in free living women.

Lean ME, Han TS, Prvan T, Richmond PR, Avenell A. University of Glasgow, Department of Human Nutrition, Glasgow Royal Infirmary, UK.
Eur J Clin Nutr 1997 Apr;51(4):243-248

This randomised controlled trial examined anthropometric changes and cardiovascular benefits of six months of weight management in 110 free living women, aged 18-68 y and BMI 25-50 kg/m2, who received 1200 kcal/d diet treatments of either high (58% energy, n = 57) or low (35% energy, n = 53) carbohydrate (CHO) content. Body weight, plasma total, HDL and LDL cholesterol, triglyceride and blood pressure were measured. Examination at three months showed women on high CHO lost (mean +/- s.e.m) 4.3 +/- 0.5 kg and those on low CHO lost 5.6 +/- 0.6 kg of body weight. Changes in risk factors did not significantly differ between the two diet treatments throughout the study. However those on high CHO diets significantly lowered their plasma total cholesterol by 0.33 mmol/l (95% CI: 0.10, 0.55), LDL cholesterol by 0.23 mmol/l (0.02, 0.43) and HDL cholesterol by 0.05 mmol/l (0.03, 0.10), while women on low CHO diets lowered only plasma triglyceride by 0.28 mmol/l (0.08, 0.48). Blood pressure did not change significantly on either diet. After six months, women on high CHO lost 5.6 +/- 0.8 kg and those on low CHO lost 6.8 +/- 0.8 kg. On the high CHO diet, total cholesterol remained significantly below the baseline value at 0.34 mmol/l (0.13, 0.56), triglyceride was significantly lowered by 0.27 mmol/l (0.10, 0.45), and HDL cholesterol returned to the baseline value. On the low CHO diet, triglyceride remained the only risk factor to be significantly improved. A subgroup of 46 postmenopausal women lost significantly (P < 0.05) more weight on the low CHO diet than high CHO diet. In conclusion, these results provided some support for preferring a high CHO diet to a lower CHO approach in weight management, from the point of view of risk reduction, but do not indicate a consistently more rapid weight loss with either diet.

Comments: 110 women were split into two groups: half got a low-carb diet, the other half, a high-carb diet. Notice that the low-carb diet wasn't very low, and the high-carb diet wasn't very high. So the two diets were almost the same. As it turns out, the women on low-carb lost about 1.20 times as much weight as the high-carb group. This isn't a very useful measurement, since we don't know if they lost fat, muscle, or water.

A randomized controlled trial of low carbohydrate and low fat/high fiber diets for weight loss.

Baron JA, Schori A, Crow B, Carter R, Mann JI
Am J Public Health 1986 Nov;76(11):1293-1296

Among 135 overweight subjects, we conducted a three-month randomized controlled trial of two sets of dietary advice, each providing approximately 1,000 calories per day but differing in fiber, carbohydrate, and fat content. Information on weight and eating habits, as well as measures of lipoprotein and glucose metabolism were obtained at entry and one and three months later. We found that dieters given low carbohydrate/low fiber dietary advice tended to lose more weight than those given a higher carbohydrate/higher fiber regimen (5.0 vs 3.7 kg on average at three months). This pattern was particularly marked among women, and among participants who were under age 40 or of lower social class. There were no differences between the diet groups in the proportion complaining of hunger but, in general, members of the low carbohydrate group complained of more problems in dieting. There were only minor differences in the serum lipoprotein patterns during the diet period. In view of these results, we believe previous claims of the benefits of fiber for weight loss may have been overstated.

Comments: they got 135 overweight people, and split them into two groups. They told half to eat 1000 calories of low-carb food. They told the other half to eat 1000 calories of high-carb food. The low-carbers lost about 1.35 times as much weight as the high-carbers.

Comparative studies in obese subjects fed carbohydrate-restricted and high carbohydrate 1,000-calorie formula diets.

Rabast U, Kasper H, Schonborn J
Nutr Metab 1978;22(5):269-277

45 obese subjects were fed a high-carbohydrate, relatively low-fat, or a low-carbohydrate, relatively high-fat 1,000-calorie (4.14MJ) formula diet. The diet provided for an isoenergetic substitution of 170 g of carbohydrates for 75 g of fat. Weight reduction up to day 30 was significantly higher in the subjects on the carbohydrate-restricted diet. There were no significant differences between the water and electrolyte balances. The mean total weight reduction achieved on the high-carbohydrate diet was 9.8 +/- 4.5kg with a mean daily weight loss of 298 +/- 80g, while the corresponding values on the carbohydrate-restricted diet were 14 +/- 7.2 kg and 362 +/- 91 g/day, respectively.

Comments: They got 45 people, and split them into two groups. The first group was given 1000 calories worth of high-carb food per day, the other group got 1000 calories worth of low-carb food per day. Both groups lost equal amounts of water weight. The low-carbers lost about 1.4 times as much real weight. They didn't mention whether that weight loss was muscle or fat.

Effects of ingestion of high protein or excess methionine diets by rats for two years.

Fau D, Peret J, Hadjiisky P Centre de Recherches sur la Nutrition, CNRS, Meudon-Bellevue, France.
J Nutr 1988 Jan;118(1):128-133

Eighteen male Wistar rats weighing 230 g (9 wk old) were fed casein diets containing 10% protein (HC), 50% protein (HP) or 10% protein plus 2% DL-methionine (MET) for 2 yr. In HC rats, mean body weight was 570 g; the carcass contained 13.5% protein and 37% lipid. The HP-fed rats had a 100 g lower body weight than HC rats due solely to a smaller amount of body lipid. Liver urea concentration and kidney weight were higher in HP rats than in HC rats. The body weight of MET-fed rats was lower than the other two groups and body lipid was only 30% that of HC rats. Histologic examination showed a normal aspect of the thoracic aorta from HC rats, whereas in HP, moderate signs of vascular aging--thicker intima and media with hypertrophy of smooth muscular cells (smc) with collagen enrichment and diffuse fibrosis--were observed. Aortas from MET rats also exhibited thicker intima and media due to smc hypertrophy. Some smc presented degenerative aspects and necrosis; other smc were replaced by chondroid cells and foci of fibrosis, resulting in a loss of the distension capacity of the aorta. Such an advanced stage of vascular aging is not normally found in 2-yr-old rats.

Comments: they fed six rats a low-protein, high-carb diet, and six rats a high-protein, moderate-carb diet. After 2 years, the low-protein, high-carb rats weighed 570 grams, the high-protein, moderate-carb rats weighed only 470 grams. The difference was entirely due to less fat.

Influence of dietary carbohydrate-to-fat ratio on whole body nitrogen retention and body composition in adult rats.

McCargar LJ, Baracos VE, Clandinin MT Department of Foods & Nutrition, Faculty of Home Economics, University of Alberta, Edmonton, Canada.
J Nutr 1989 Sep;119(9):1240-1245

Experiments have shown that the amount and source of dietary energy may alter protein metabolism. A high fat diet has resulted in greater nitrogen retention than a high carbohydrate (CHO) diet. To examine this question further, adult rats were fed diets providing ratios of CHO:FAT as a percentage of energy of 0.5, 1.0, 1.5, 2.0, 2.5 or 3.0 for 6 wk. Mean energy and protein intakes were 93.0 +/- 0.8 kcal/d and 5.3 +/- 0.1 g/d, respectively. Final body weight was lower in rats fed the high fat diet (CHO:FAT, 0.5) than in rats fed the high carbohydrate diet (CHO:FAT, 3.0) (P less than 0.05), and a linear response was observed over the entire range of treatments (r = 0.92). Rats fed the high fat diet had the highest nitrogen balance; values were significantly (P less than 0.05) different from those of rats fed high carbohydrate diets (CHO:FAT, 2.0 or 2.5) when expressed as mg nitrogen/kcal energy gain. Rats fed the high fat diet had the highest protein gain and the lowest fat gain as a function of energy gain. It is concluded that alterations in nonprotein energy source result in metabolic changes, which may be related to adaptations in energy expenditure and/or protein deposition.

Comments: They got a bunch of rats and divided them into several groups. All groups received the same number of calories, and the same amount of protein. Some groups got lots of fat, other groups got lots of carbs, and some were in-between. The less carbs they got, the less fat they turned out to be. And the less carbs they got, the more muscular they turned out to be.

Similar weight loss with low- or high-carbohydrate diets.

Golay A, Allaz AF, Morel Y, de Tonnac N, Tankova S, Reaven G. Department of Medicine, Geneva University Hospital, Switzerland.
Am J Clin Nutr 1996 Feb;63(2):174-178

The goal of this study was to evaluate the effect of diets that were equally low in energy but widely different in relative amounts of fat and carbohydrate on body weight during a 6-wk period of hospitalization. Consequently, 43 adult, obese persons were randomly assigned to receive diets containing 4.2 MJ/d (1000 kcal/d) composed of either 32% protein, 15% carbohydrate, and 53% fat, or 29% protein, 45% carbohydrate, and 26% fat. There was no significant difference in the amount of weight loss in response to diets containing either 15% (8.9 +/- 0.6 kg) or 45% (7.5 +/- 0.5 kg) carbohydrate. Furthermore, significant decreases in total body fat and waist-to-hip circumference were seen in both groups, and the magnitude of the changes did not vary as a function of diet composition. Fasting plasma glucose, insulin, cholesterol, and triacylglycerol concentrations decreased significantly in patients eating low-energy diets that contained 15% carbohydrate, but neither plasma insulin nor triacylglycerol concentrations fell significantly in response to the higher-carbohydrate diet. The results of this study showed that it was energy intake, not nutrient composition, that determined weight loss in response to low-energy diets over a short time period.

Comments: they got 43 people, and split them into two groups. One group got 1000 calories of low-carb food, the other group got 1000 calories of moderate-carb food. The low-carbers lost 1.2 times as much weight.

Glucose utilization and nitrogen balance in the obese on a protein-lipid hypocaloric diet.

Reid D, Rasio E
Can J Physiol Pharmacol 1982 Mar;60(3):319-323

Glucose utilization and insulin and growth hormone responses were evaluated in eight obese women by three rapid intravenous glucose tolerance tests (IVGTT): during a control period, and after 1 and 3 weeks of a 750 kcal/day protein-lipid diet (1 kcal = 4.1855 kJ). Weight loss averaged 454 g/day during the 1st week and 238 g/day for the 2nd and 3rd weeks of the diet. Nitrogen balance was maintained in equilibrium. Plasma insulin concentrations fell by 50% within 1 week of dieting; growth hormone levels were not modified. The net rate of glucose disappearance dropped from 0.98 to 0.65 and 0.68% min, the glucose pool from 16.2 to 13.3 and 13.4 g, and glucose utilization from 158 to 88 and 87 mg/min during the control period, and at 1 and 3 weeks of dieting, respectively. The insulinogenic index decreased from 0.41 to 0.24 to 0.16 with successive IVGTT's. The glucose volume of distribution was not modified with dieting. It is concluded that a hypocaloric protein-lipid diet induces (i) a carbohydrate intolerance not related to a negative nitrogen balance and (ii) a rapid initial weight loss which cannot be ascribed to a depletion of the glucose volume.

Comments: Does this mean what I think it means? As far as I can tell, it seems to be saying: They gave some people a low-carb diet. They discovered that the glycogen stores were (surprisingly) only depleted a little bit. They noticed the rapid weight loss on induction, and they concluded (since glycogen barely moved) that it wasn't caused by glycogen depletion. Is this right? Am I understanding this?