Carb Wars: Are Carbs Bad for Your Physique
by: Robbie Durand
In recent years, low carb diets have become more popular. Low carb proponents claim that the resulting decreased insulin secretion causes elevated release of free fatty acids from adipose tissue, increased fat oxidation and energy expenditure, causing greater body fat loss than restriction of dietary fat.
While clinical weight loss trials have typically found that low carbohydrate diets cause greater short-term weight loss, there are very few long-term studies conducted on low carb vs. low fat diets. This isn’t going to be easy for low carb dieters to read this, but in a paper published August 13 in Cell Metabolism, titled, “Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity” the researchers show how, contrary to popular claims, restricting dietary fat or low fat diets can lead to greater body fat loss than carb restriction, even though a low-carb diet reduced insulin and increased fat burning.
The researchers studied 19 non-diabetic men and women with obesity in the Metabolic Clinical Research Unit at the NIH Clinical Center in Bethesda, Maryland. Participants stayed in the unit 24 hours per day for two extended visits, eating the same food and doing the same activities. For the first five days of each visit they ate a baseline balanced diet. Then for six days, they were fed diets containing 30 percent fewer calories, achieved by cutting either only total carbs or total fat from the baseline diet, while eating the same amount of protein. They switched diets during the second visit. So basically they were placed on both a low carb and a low fat diet with equal. The scientists used a mathematical model to predict long-term weight loss based off the subject’s responses to diets while they sat in a metabolic chamber.
So what happened at the end of the study? Daily energy expenditure decreased similarly on low-carb diet and low fat diets, but more weight was lost with low-fat diet vs. low-carb diet. Here is where it gets really interesting!
Low Carb Diets Resulted in Greater Fat Oxidation and Lower Insulin levels, but not Greater Weight Loss.
Whole-body fat oxidation rapidly increased during the low-carb diet, but was unchanged on the low fat diet. In contrast, the low fat diet demonstrated no change in fat oxidation despite reducing fat intake by ~800 kcal/day. While fat oxidation during prolonged low-fat and low-carb diets would be expected to slowly decrease over time, the researchers suggest the low-fat diet will lead to more long-term body fat loss than with the low-carb diet.