Nutrition Performance - Low-Carb Diets: A Research Update

"The view that the sun stands motionless at the center of the universe is foolish, philosophically false, utterly heretical, because it is contrary to Holy Scripture. The view that the earth is not the center of the universe and even has a daily rotation is philosophically false, and at least an erroneous belief. "

— Holy Office, Roman Catholic Church, edict of March 5, 1616

When Galileo claimed the world goes around the sun, he was forbidden by the pope to continue such “heretical teaching.” Writing to Copernicus, Galileo said, “They will not even look in my telescope.” It’s easy to think such rigid beliefs could not possibly occur in the modern scientific community, yet they certainly do. When it comes to nutritional sciences, some narrow-minded nutritionists simply ignore well-controlled studies reporting positive effects of high-protein/low-carb diets. Clearly, these malcontent mavericks find the results of these studies too disturbing as they relate to their preconceived ideas.

A 2003 commentary by the American Heart Association´s (AHA) low fat proponents published in the respected New England Journal of Medicine provides a perfect example of this ridiculous reluctance: “In both studies, the reduction in serum triglyceride [harmful blood lipids] levels in subjects randomly assigned to the low-carbohydrate diet might have been anticipated as a result of their greater weight loss, although it is true that reduced carbohydrate intake is generally associated with reduced triglyceride levels.”

So, despite the fact that reduced carb intake decreases triglyceride levels, the authors of this piece desperately try to suggest otherwise.

Furthermore, they suggest, without any evidence, that “the rise in HDL cholesterol [good cholesterol] in the subjects following the low-carbohydrate diet may reflect a change in HDL subfractions that occurs with increased intake of saturated fats, and this change has not been shown to be beneficial.”

We now know, however, that the most consistent effect of the low-carb diet is a remarkable decrease in triglycerides, and this response is not explained by changes in bodyweight. Also, compared with the low-fat diet (i.e., AHA diet), the very-low-carb diet results in a significant increase in good cholesterol (HDL). Finally, it has been observed that very low carb intake can induce a significant increase in bad cholesterol (LDL) particle size; larger LDL particles are associated with a lower risk for heart disease.

So, the commentary by AHA people was pseudo-scientific nonsense. A smart scientist said a long time ago: “New ideas are always criticized, not because an idea lacks merit, but because it might turn out to be workable, which would threaten the reputations of many people whose opinions conflict with it. Some people may even lose their jobs.”

Why Does a Low-Carb Diet Promote Fat Loss?

Several studies have shown increased weight loss/fat loss on low-carb diets compared to isocaloric high-carb/low-fat diets. However, it is not clear why a low-carb diet is so effective. To study this mystery, Dr. Bonnie Brehm and co-workers at the University of Cincinnati, Ohio, randomized 50 healthy, moderately obese women to four months of an ad libitum (self-directed) low-carb diet or an energy-restricted, low-fat diet.¹ Resting energy expenditure was measured at baseline, two months and four months. Also, the thermogenic effect of food in response to a low-carb and low-fat breakfast was assessed over five hours in a subset of subjects.

As expected with the loss of bodyweight, the results showed a reduction in resting energy expenditure in both groups over the course of study. However, resting energy expenditure did not significantly differ between the groups at baseline or at the two- and four-month assessments. Further, it was a surprise that the low-fat diet caused a greater five-hour increase in thermogenesis than the low-carb meal. As pointed out by the authors, however, the low-carb meal is absorbed more slowly than the high-carb meal, so it’s plausible that the five-hour period the investigators used to measure thermogenesis may have underestimated the full thermogenic effect of the low-carb diet. Whatever the case, this study confirmed that weight loss is greater in obese women on a low-carb diet than in those on a low-fat diet, even when the reported calorie intake is similar.

New Atkins Study

Dr. Guenther Boden and collegues at Temple University Hospital in Philadelphia designed a study to determine the effects of a very-low-carb (ketogenic) diet (about 20 grams of carbs per day), which included the dietary supplements recommended by Dr. Atkins, on the following: energy intake and expenditure, bodyweight and body water, sugar metabolism and insulin sensitivity.² Ten obese patients with type 2 diabetes participated in this study. The investigators excluded volunteers who had other significant health problems. Before hospitalization, an investigator interviewed all study participants about their recent diet and exercise habits.

During days one to seven, the investigators instructed subjects to continue their usual diet. During days eight to 21, the subjects reduced their carb intake to about 20 grams— but they could eat protein and fat as much and as often as they wanted. Nevertheless, the mean caloric intake decreased by about 1,000 calories a day. Consequently, the mean bodyweight decreased by 2.02 kilograms (4.4 pounds). Corrected for changes in body water, the mean weight (fat) loss was 1.65 kilograms (3.63 pounds). Sugar profiles and insulin sensitivity also improved and there were no adverse effects on kidney function or blood lipids. In summary, this short-term study showed that a very-low-carb diet is a very effective and safe approach to fat loss.

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