Time for some more science! Today I will be summarizing an article entitled
A Lower-Carbohydrate, Higher-Fat Diet Reduces Abdominal and Intermuscular Fat and Increases Insulin Sensitivity in Adults at Risk of Type 2 Diabetes
In this study, authors evaluated fat loss in 69 overweight/obese men and women aged 21-50 years assigned to 1 of 2 diets, and 30 women with polycycstic ovary syndrome (PCOS) assigned to both diets with a crossover design.
The authors included ONLY African American or European American overweight/obese people without diabetes and whose weight hadn’t changed more than 2.3kg over the past 6 months. They excluded participants who exercised more than 2 hours/week, smoked, were pregnant or breastfeeding, or using any medication that could affect body composition (including hormonal birth control).
For the first 8 weeks, participants were assigned to 1 of 2 eucaloric (meaning they were intended to be at maintenance calorie intake – not intended for weight loss/gain) diets . We’ll call this the maintenance phase.
1) 55% carbohydrate, 27% fat, 18% protein
2) 43% carbohydrate, 39% fat, 18% protein
For the second 8 weeks, total calorie intake was decreased by 1000kcal/day, while macronutrient balance was maintained. This will be the weight loss phase
The two groups were compared in terms of body fat mass, fat around the midsection, and markers of inflammation
On fat mass/ fat around the midsection
In the maintenance phase
Participants in the lower carbohydrate group lost significantly (11%) more fat around the midsection, even when adjusted for starting levels of fat mass!
In the weight loss phase
Participants in the lower carbohydrate group lost significantly more (4.4%) fat mass than patients in the low fat group. Again, this is while adjusting for initial fat mass levels.
At the end of the full 16 weeks, participants in the low carbohydrate group lost approximately 6kg (or ~13 pounds), compared to 4kg (~8 pounds) in the low fat group. Keep in mind that this is only 4 weeks of caloric deficit.
On markers of inflammation
No change was observed in either group, for either phase on markers of inflammation
The results were not different between ethnic groups (meaning both African Americans, and European Americans experienced the same effects – more fat loss in the low-carbohydrate group)
Women with PCOS
The authors included only women diagnosed with PCOS between 21-50 years with a super obese BMI (greater than or equal to 45). Other inclusion/exclusion criteria were the same as above.
The women were assigned to one of the two diets for 8 weeks, followed by a 4 week washout period (participants were not assigned to any specific diet and were not given any specific foods), and then assigned to the opposite diet for another 8 week period.
While in the low-carbohydrate phase, participants lost significantly more fat around the midsection and fat mass compared to the low-fat phase (while adjusting for initial fat mass and change in lean mass). Also interesting: while in the low fat phase, participants lost significantly more lean body mass (read:muscle mass) compared to the low-carbohydrate phase.
Limitations of this study include the exclusion of participants with diabetes, taking hormonal birth control and other ethnicities, which could have made up a large portion of the population untested.
Additionally, for the PCOS study cross over design, they did not report the what participants ate during the washout period, which could have contaminated the results (for example, if participants were assigned to the low-carbohydrate group in the first phase, it is possible that they could have eaten a ton of carbs during the washout period – after restricting them – which could have resulted in lower fat loss in the second phase of the study).
Authors also did not record participant activity level throughout the study, which could have confounded the results, and although food was provided for the duration of the study (which is a big strength in these types of studies!), they did not specify where participants were getting their macronutrients from (i.e. carbs from fruits/veggies vs. chips, protein/fat sources).
It looks like restricting carbohydrate composition is more effective in terms of fat loss compared to restricting carbohydrates, even while maintaining your daily calorie intake!
But remember – this isn’t evidence for eating whatever you want as long as it’s low in carbs and high in fat. A lot of other factors do contribute to weight/fat loss in the general population, including total calorie intake, exercise, metabolism, size, etc. It should also be noted that the percentage of carbohydrate intake even in the low-carb group was not extreme. We’re not talking ketosis here – just watching overall carb intake and not restricting good fats.
If you’re looking to lose weight make sure you’re eating mostly fruits and vegetables as your carbohydrate sources, and don’t be afraid to eat a little peanut butter (or avocado, or nuts, or olive oil)!
Citation: Gower, B. A. and A. M. Goss (2015). “A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes.” J Nutr 145(1): 177s-183s.