Low-fat, Low-glycemic And Low-carb Diets Compared

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A low-fat diet may put people at the highest risk for gaining their weight back, because it decreases their resting energy expenditure and total energy expenditure more than other diets, such as a low-glycemic index diet and a very low carbohydrate diet. A team of investigators from Children’s Hospital Boston published their preliminary research in JAMA while studying the effects on energy expenditure and components of the metabolic syndrome of these 3 common diets.

A low-fat diet requires a limited amount of fat, most importantly saturated fat, cholesterol, and total caloric intake. This diet typically limits to 1700 calories per day. Foods high in carbohydrates are recommended.

A low-glycemic index diet measures the amount of carbohydrate intake. The diet follows a scale where food is assigned an index number from 1-100 (100 meaning pure glucose). Eating low-glycemic foods take longer for the body to absorb, which makes the person feel satisfaction longer and be less likely to overeat.

A very low carbohydrate diet restricts carbohydrates to about less than 20% of caloric intake per day. Foods containing a higher percentage of proteins and fats are eaten in place of foods such as pasta and bread (foods high in carbohydrates).

Dieters struggle to keep the weight off

Many people struggle with weight loss and understand how hard it is to keep the weight off. Unfortunately, these dieters do not know the reasons they put their weight back on and keep trying different diets to find the long-term results they are looking for.

The researchers explain as background information to their report:

“Many people can lose weight for a few months, but most have difficulty maintaining clinically significant weight loss over the long term. According to data from the National Health and Nutrition Examination Survey (1999-2006), only 1 in 6 overweight and obese adults report ever having maintained weight loss of at least 10 percent for 1 year”.

Feet on scale
The problem is not losing the weight, but keeping it off

We lose weight, use less energy, get hungry and put the weight back on

One explanation is that losing weight causes a decline in energy expenditure, while increasing hunger eventually results in weight gain.

In order to evaluate the effects of dietary composition on energy expenditure during weight loss, Carl B. Ebbeling, Ph.D., of Children’s Hospital Boston, and colleagues conducted a study using the 3 different weight-loss maintenance diets mentioned above. The study tested the diets on energy expenditure, hormones, and components of the metabolic syndrome between June 2006 sand June 2010.

The study consisted of 21 young adults, either overweight or obese, who achieved 10 percent to 15 percent weight loss while trying a run-in diet. The participants then were chosen one of the 3 diets in random order, each for 4 weeks. The diets were the low-fat diet (high glycemic load), low-glycemic index diet (moderate glycemic load), and very low-carbohydrate diet (low glycemic load). Resting energy expenditure (REE), total energy expenditure (TEE), hormone levels, and metabolic syndrome components were all measured.

There was a significant difference in the energy expenditure during weight-loss in each of the 3 diets. Researchers found that:

  • The decrease in REE from pre-weight loss levels was greatest for the low-fat diet (average relative to baseline, -205 kcal/d) while measured by indirect calorimetry in the fasting state.
  • The very-low carbohydrate diet showed the least amount of decrease (-138 kcal/d)
  • The low-glycemic diet showed intermediate decreases in the low-glycemic index diet.
  • Each diet also showed significant decreases in TEE:
    – average -423 kcal/d for low fat
    – average 297 kcal/d for low glycemic index
    – average 97 kcal/d for very low carbohydrate

Findings challenged that notion that a calorie is a calorie

The authors said:

“Hormone levels and metabolic syndrome components also varied during weight maintenance by diet (leptin; 24-hour urinary cortisol; indexes of peripheral and hepatic insulin sensitivity; high density lipoprotein [HDL] cholesterol; non-HDL cholesterol; triglycerides; plasminogen activator inhibitor 1; and C-reactive protein), but no consistent favorable pattern emerged.

The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective. TEE differed by approximately 300 kcal/d between these 2 diets [very low-carbohydrate vs. low-fat], an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity.

(Conclusion) These findings suggest that a strategy to reduce glycemic load rather than dietary fat may be advantageous for weight-loss maintenance and cardiovascular disease prevention. Ultimately, successful weight-loss maintenance will require behavioral and environmental interventions to facilitate long-term dietary adherence. But such interventions will be most effective if they promote a dietary pattern that ameliorates the adverse biological changes accompanying weight loss.”