Written by Anssi Manninen, MHS
30 October 2006
Focus on Extra Lard 
The Story Continues...

 

"People think it must be fun to be a super genius, but they don't realize how hard it is to put up with all the idiots in the world."- Calvin (in "Calvin and Hobbes")

 "A calorie is a calorie, regardless of where it comes from," says Dr. Elizabeth Pivonka, president of the Produce for Better Health Foundation. However, this assumption is clearly fallacious. Numerous studies show that calorie content may not be as predictive of fat loss as is reduced carbohydrate consumption. This article separates the facts from the street noise.

 

A Calorie is Not a Calorie!

            Dr. F. Samaha and coworkers randomly assigned 132 severely obese subjects to a low-carbohydrate or calorie- and fat-restricted (low-fat) diet. Seventy-nine subjects completed this six-month study. It should be noted that the difference in consumption of energy from carbohydrate was quite narrow: 51 percent in the low-fat group and 37 percent in the low-carbohydrate group. Total energy intake at the six-month mark was 1,567 calories per day in the low-fat group and 1,630 in the low-carbohydrate group. Thus, the low-carbohydrate group consumed 54 extra calories per day. Nevertheless, the low-carbohydrate group lost 5.8 kilograms (13.8 pounds) and was still losing weight at six months, vs. 1.9 kilograms (4.2 pounds) in the low-fat group, whose weight had leveled off).

            Dr. B. Brehm and colleagues 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 six months of either an ad libitum (self-supervised) very-low-carbohydrate diet or a calorie-restricted diet with 30 percent of the calories as fat. Fifty-three healthy, obese female volunteers were randomized; 42 completed the trial. Both groups were free-living and had reduced energy intake by similar amounts at three and six months, but the low-carbohydrate group lost more weight (8.5 kilograms vs. 3.9 kilograms, or 18.7 pounds vs. 8.6 pounds) and more body fat (4.8 kilograms vs. 2.0 kilograms, or 10.5 pounds vs. 4.4 pounds). Their results also indicated that the weight loss in the low-fat groups was leveling out, while the loss in the low-carbohydrate groups was continuing. According to authors, "It is difficult to explain the differences in weight loss between the two groups primarily as a function of differing caloric intake."

            In a randomized, controlled 12-week trial, Dr. S. Sondike and co-workers compared the effects of a low-carbohydrate diet with those of a low-fat diet on weight loss and serum lipids in overweight adolescents. The low-carbohydrate group was instructed to consume less than 20 grams of carbohydrate per day for two weeks, then less than 40 grams per day for 10 weeks, and to eat low-carbohydrate foods according to hunger. The low-fat group was instructed to consume less than 30 percent of energy from fat. The results indicated that the low-carbohydrate group lost 9.9 kilograms (21.8 pounds) vs. 4.1 kilograms (9.0 pounds) for the low-fat group, despite both the lower initial weight of the low-carbohydrate group (92.1 kilograms vs. 99.5 kilograms, or 212.6 pounds vs. 218.9 pounds) and the disparity in calories in favor of the high-carbohydrate group.

            Harvard researchers found that people eating an extra 300 calories a day on a very-low-carbohydrate diet lost a similar amount of weight during a 12-week study to those on a low-fat diet. Over the course of the study, subjects consumed an extra 25,000 calories that should have added up to about a seven-pound weight gain; it did not. The study was unique because all the food was prepared at an upscale Italian restaurant, so the researchers knew exactly what the subjects ate, and one could not argue that the diets were not palatable.

            Finally, a recent randomized, balanced, two-diet study compared the effects of isocaloric, energy-restricted ketogenic and low-fat diets on weight loss and body composition in overweight/obese men and women. Despite significantly greater calorie intake (1,855 vs. 1,562 calories per day), both between- and within-group comparison revealed a distinct advantage of a ketogenic diet over a low-fat diet for weight loss/fat loss for men. In fact, five men showed more than 10 pounds difference in weight loss. A majority of the women also responded more favorably to the ketogenic diet, especially in terms of trunk fat loss.

            Furthermore, the individual responses revealed that three men and four women who did the ketogenic diet first, regained body mass and fat mass after the switch to the low-fat diet, whereas no subjects regained weight or fat mass after switching to the ketogenic diet. The authors concluded, "This study shows a clear benefit of a [ketogenic diet] over a [low-fat] diet for short-term bodyweight and fat loss, especially in men." (Free full text article of this study is available at www.nutritionandmetabolism.com/content/pdf/1743-7075-1-13.pdf)

 

"Don't Confuse Me with the Facts, it's Just Water"

            Although the greater weight loss has obvious significance, at least equally important is the question related to the composition of weight loss. In 1965, Dr. F. Benoit and colleagues published the first systematic study of the effect of a very-low-carbohydrate (ketogenic) diet on composition of weight loss. They observed that when a 1,000-calorie ketogenic diet (10 grams of carbohydrates per day) was fed for 10 days, their seven male subjects lost an average of 600 grams per day, of which 97 percent was fat. However, the energy value of the tissue loss reported by Dr. Benoit is about 7,000 calories per day, a highly improbable level of energy expenditure for subjects confined to a metabolic chamber.

            In 1971, Dr. C. Young and co-workers compared three diets containing the same amount of energy (1,800 calories per day) and protein (115 grams per day) differing in carbohydrate content (30, 60 and 104 grams per day). After nine weeks on the 30-, 60- and 104-gram carbohydrate diets, weight loss was 16.2, 12.8, and 11.9 kilograms (35.6, 28.2 and 26.2 pounds) and fat accounted for 95, 84 and 75 percent of the weight loss, respectively.

            More recently, Dr. J. Volek and colleagues examined the effects of a six-week very-low-carbohydrate diet on total and regional body composition. Interestingly, their results indicated that fat mass was significantly decreased (-3.4 kilograms, or -7.5 pounds) and lean body mass significantly increased (+1.1 kilograms, or 2.4 pounds) at week six. As expected, a very-low-carbohydrate diet led to a significant decrease in blood insulin concentrations and there was a significant correlation between the decrease in insulin and the decrease in body fat, indicating that fat tissue breakdown was up-regulated, which was also supported by the elevated ketone body concentrations.

            Dr. S. Willi and co-workers examined the efficacy and metabolic impact of a ketogenic diet in the treatment of morbidly obese adolescents. The authors concluded that a ketogenic diet is "a safe and effective weight loss regimen... The weight loss with this approach is rapid, consistent and almost exclusively from body fat stores." 

            Nevertheless, it's frequently claimed that additional weight loss with low-carbohydrate diets can be entirely explained by dehydration. However, the classic study by Dr. U. Rabast and colleagues demonstrated that alterations in the water balance observed during the low-carbohydrate diets are reversible phenomena and should thus not be regarded as causal agents in the different weight reductions. Also, modern studies that measured body composition by dual-energy X-ray absorptiometry didn't find any indication of excessive reduction in lean body mass. So, the greater weight loss is attributable to fat loss.

 

            New Study: A Ketogenic Diet is Safe

            Recently, Dr. H. Dashti and colleagues examined the effects of a 24-week ketogenic diet consisting of 30 grams of carbohydrate, one gram per kilogram of bodyweight of protein, 20 percent saturated fat and 80 percent polyunsaturated and monounsaturated fat. Investigators selected 83 obese patients (39 men and 44 women) with a body mass index greater than 35 kg/m2 and high glucose and cholesterol levels.

            The results indicated that the weight and body mass index of the patients decreased significantly. Also, the level of total cholesterol decreased from week one to week 24. Good cholesterol (HDL) levels significantly increased, whereas bad cholesterol (LDL) levels significantly decreased after treatment.

Finally, triglycerides (harmful blood lipids) and the level of blood sugar decreased significantly. Importantly, the changes in the level of urea and creatinine were not significant, suggesting a ketogenic diet had no adverse effects. According to the authors, "The present study confirms that it is safe to use a ketogenic diet for a longer period of time than previously demonstrated."

 

Bottom Line

It's now clear that the idea that "a calorie is a calorie" is nonsense. In fact, the calorie content may not be as predictive of fat loss as is reduced carbohydrate consumption. However, there will be some metabolic accommodations and one cannot assume that the metabolic advantage (i.e., greater weight loss compared to isocaloric high-carbohydrate diet) will stay the same over a long term. The ideal weight loss diet, if it even exists, remains to be determined, but a high-carbohydrate/low-protein diet is not the way to go.

 

References

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