Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake.
Level 2 - randomized trial
Randomized crossover clinical trial
PubMed 33479499 · doi:10.1038/s41591-020-01209-1
What was done
Twenty adults (mean age 29.9 ± 1.4 years, BMI 27.8 ± 1.3 kg m⁻²) were admitted as inpatients to a clinical research center and randomized to consume ad libitum either a minimally processed plant-based low-fat diet (10.3% fat, 75.2% carbohydrate) or an animal-based ketogenic diet (75.8% fat, 10.0% carbohydrate) for 2 weeks, followed immediately by the alternate diet for 2 weeks. The primary outcome was mean daily ad libitum energy intake across the 2-week period and during the final week of each diet.
What was found
The low-fat diet resulted in 689 ± 73 kcal d⁻¹ less energy intake than the ketogenic diet over the full 2 weeks (P < 0.0001) and 544 ± 68 kcal d⁻¹ less over the final week (P < 0.0001).
Why it matters
These findings contradict the carbohydrate-insulin model of obesity, demonstrating that a high-carbohydrate, low-fat diet did not stimulate higher ad libitum energy intake compared to a ketogenic diet in tightly controlled conditions.
Limits
The sample size was small (n = 20) with a brief intervention period of 2 weeks per diet phase. Inpatient feeding restricts generalizability to free-living populations, long-term outcomes were not evaluated, and one participant withdrew due to hypoglycemia during the ketogenic diet.
Cited by
- supports In Kevin Hall's 2021 ad libitum feeding study, subjects on a plant-based high-carbohydrate diet spontaneously consumed approximately 700 fewer calories per day than those on a ketogenic diet.