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One Diet Does Not Fit All: Weight Loss Study

Obesity is a major health challenge and there is a debate regarding whether a low-fat or a low-carbohydrate diet is the most effective approach for weight loss. There is limited preliminary evidence that matching the diet to a genotype pattern relevant to fat and carbohydrate metabolism may improve weight loss. The aim of this study was to determine whether a putative genotype pattern (low-fat vs. low-carbohydrate), or insulin-secretion (related to insulin resistance), would help to explain which diet is best for whom in a comparison of a healthy low-fat to a healthy low-carb diet over a one-year period, in generally healthy, non-diabetic, overweight and obese adults.

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Eligible Participants

  • Generally healthy men and premenopausal women, 18 to 50 years of age
  • Overweight or obese
  • Interested in losing weight
  • Willing to be randomly assigned to follow either a low-fat or low-carbohydrate diet for 12 months

Study Design

Six hundred and nine participants were randomly assigned to follow a healthy low-fat diet or a healthy low-carbohydrate diet for 12 months. During the study, they received 22 instructional sessions with a registered dietitian, weekly for the first 8 weeks, then every 2 weeks for 2 months, then every 3 weeks until the sixth month, and monthly thereafter. Participants were instructed to reduce their intake of total fat or digestible carbohydrate to 20 grams per day during the first 8 weeks. They then slowly added fats or carbohydrates back to their diets in increments of 5 to 15 g/d per week until they reached the lowest level of intake they believed could be maintained indefinitely. Both groups were instructed to focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible. They completed clinic visits after 3, 6, and 12 months to asses weight, energy expenditure, and various markers of cardiometabolic health.

Conclusions

After one year, participants lost, on average, 12 pounds on the healthy low-fat diet and 13 pounds in the healthy low-carb diet. The results showed no significant difference in weight change between the two diet groups, and neither the specific genotype pattern nor baseline insulin secretion levels were helpful in identifying which diet was better for whom. However, the range of weight change within both diet groups was dramatic – from losing ~60 pounds to gaining ~20 pounds.

Research