Lower energy intake observed in low-fat vegan vs. low-carb ketogenic diet
A cohort of adults had less energy intake when eating a low-fat, plant-based diet compared with an animal-based, low-carbohydrate ketogenic diet during a 2-week period, according to study data published in Nature Medicine.
According to Kevin D. Hall, PhD, integrative physiology section chief at the National Institute of Diabetes and Digestive and Kidney Diseases, the study’s findings run counter to the carbohydrate-insulin model of obesity, which suggests that increasing levels of insulin stemming from the consumption of high-carbohydrate foods leads to excess fuels being stored in fat cells and not being available for use by other organs, thereby resulting in those organs experiencing a state of cellular starvation resulting in increased hunger and calorie intake.
“The take-home message here is that we got exactly the opposite results of what was predicted by the carbohydrate-insulin model,” Hall told Healio. “People ate much less calories, despite having very high levels of insulin after meals, and they lost body fat.”
Hall and colleagues conducted a crossover study with 20 adults without diabetes who stayed at the Metabolic Clinical Research Unit at the NIH Clinical Center for 4 weeks. In random order, participants spent 2 weeks each consuming an animal-based, ketogenic, low-carbohydrate diet in which 10% of energy came from carbohydrates and 75% from fat; and a plant-based, low-fat diet with 10% of energy from fat and 75% from carbohydrates. Both diets were low in ultra-processed foods and matched for nonstarchy vegetables. Daily meals and a continuous supply of snacks and water were provided. Daily food and beverages were provided at twice each participant’s estimated baseline energy requirements. The primary outcomes were the difference in mean energy intake between each two-week diet period and the difference in mean energy intake during only the second week of each diet.
There were 11 men and nine women who participated in the study (mean age, 29.9 years; mean BMI, 27.8 kg/m2). The low-fat diet resulted in a mean energy intake of 689 kcal per day less than the low-carbohydrate diet over the two-week test period (P < .0001). During the second week of each diet period, those on the low-fat diet had a mean of 544 kcal per day less energy intake than those on the low carbohydrate diet.
Participants reported no preference for one diet over the other. There were no differences in the pleasantness of the diets or food familiarity. The study population also reported no significant differences in hunger, satisfaction, fullness or eating capacity.
Hall noted that the findings run contrary to the carbohydrate-insulin model, but they also do not fully support the passive-overconsumption model of obesity, which posits that high-fat diets (like the low-carbohydrate diet in this study) lead to excess calorie intake and gains in body fat. The study’s findings showed body fat did not significantly change at the end of the low-carbohydrate diet.
“Our data clearly don’t support the carbohydrate-insulin model,” Hall said. “They also don’t really support the passive-overconsumption model. Neither of these models are sufficient to explain why people overeat and gain weight.”
Hall noted that this study was not a weight loss study and that each diet resulted in some metabolic improvements in participants, and each may have its own uses for specific individuals.
“It’s not that one diet won over the other,” Hall said. “It’s that these simple models of what determines people’s food intake didn’t pan out, and in particular, the data was very clearly in the opposite direction of the carbohydrate-insulin model.”
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Kevin D. Hall, PhD, can be reached at email@example.com.