A Comparison: Low-Fat, Plant-Based Diet Vs. Low-Carb, Animal-Based Diet


Most people seem to assume that weight gain and obesity are caused by a lack of willpower, which is not entirely true. Although weight gain primarily results from eating behavior and lifestyle, some people are at a disadvantage when controlling their eating habits. The increasing prevalence of obesity can also be blamed on the aggressive marketing of heavily processed foods whose quality, quantity, and composition have changed over time to promote excess energy intake and get people hooked. 

In line with this, several diet-based interventions aimed to foster weight loss for people with obesity are being utilized. There are two competing models of obesity introduced, but their treatment contrasts the relative roles of dietary fat versus carbohydrate.

A study at the National Institutes of Health looked into these two models of obesity and determined whether high-carb or high-fat diets result in greater calorie intake. The findings of the study published in Nature Medicine widen the understanding of how restricting dietary carbohydrates or fats may affect health. This article will explore some of the study’s essential findings and show how a low-fat, plant-based diet and a low-carb, animal-based diet differ.

Comparing Low-Fat, Plant-Based Diet to Low-Carb, Animal-Based Diet

The carbohydrate-insulin mode is heightened after consuming high-glycemic carbohydrates, which is thought to encourage the storage of body fat and thus increase hunger and energy intake.

On the other hand, high-fat foods may encourage excess passive energy consumption because of their high energy density, lack of satiation and satiety, and altered food hedonics that enable higher intake.

LC, ketogenic diet proponents frequently advise avoiding foods high in sugar and starch and consuming a range of non starchy vegetables and animal sources instead.

While eliminating oils, cooking fats, and spreads, proponents of LF diets frequently suggest “whole food” plant-based meals that contain non starchy vegetables and whole grains, legumes, and starchy vegetables.

The 2021 National Institutes of Health study aimed to resolve the long-running controversy about whether eating low-carbohydrate (LC) or low-fat (LF) diets is beneficial for appetite control.

What The Research Found

Twenty healthy persons without diabetes were accommodated by the researchers at the Metabolic Clinical Research Unit of the NIH Clinical Center for four weeks. Eleven men and nine women were given either a low-fat, plant-based diet or a low-carbohydrate, animal-based diet for two weeks, followed by another two weeks on the opposite diet. The low-fat diet had a lot of carbs.

The diet was low in carbohydrates but heavy in fat. Both diets contained an equal amount of non-starchy veggies and had a limited amount of processing. The participants get three meals and two snacks daily and are free to consume as much as they like.

The animal-based, low-carb diet had 10% carbohydrate and 75.8% fat, whereas the plant-based, low-fat diet had 10.3% fat and 75.2% carbohydrate. Both diets included roughly 14% protein and provided the subjects with the same number of calories overall, but the low-carb diet had twice as many calories per gram of food as the low-fat diet. A baked sweet potato, chickpeas, broccoli, and oranges can be found on the low-fat menu, while beef stir-fry with cauliflower rice might be on the low-carb menu. Of the meals provided, subjects were free to consume as much or as little as they pleased.

Based on their analysis, the researchers discovered that:

“People on a low-fat, plant-based diet ate fewer daily calories but had higher insulin and blood glucose levels, compared to when they ate a low-carbohydrate, animal-based diet”

  • People who followed a low-carb diet consumed 550–700 fewer calories each day than those who followed a low-fat diet.
  • Participants reported no variations in hunger, enjoyment of meals, or fullness across the two diets, despite the significant differences in caloric consumption.
  • Both diets resulted in weight loss for the participants, but only the low-fat diet significantly reduced body fat.
  • Despite being high in fat, the animal-based, low-carb diet did not cause weight gain.

These findings imply that factors other than the quantity of fat or carbohydrates in a person’s diet contribute to overeating and weight gain. The results also point to short-term advantages for both diets. The animal-based, low-carb diet leads to lower and more stable insulin and glucose levels, whereas the low-fat, plant-based diet aids in hunger suppression.

The researchers caution that the results might have been different if participants had been actively trying to reduce weight, as the study was not intended to offer diet advice. Additionally, all meals were made and given to participants in an inpatient environment, which may make it difficult to replicate the results outside of the lab, where issues like food costs, food availability, and meal preparation limitations can make it challenging to stick to a diet.

In sum, the results suggest that the regulation of energy intake is more complex than these and other simple models propose. Further research may be needed to verify if the study results would have been different in free-living people actively trying to lose weight. However, the researchers stated that this study is a step closer to answering long-sought questions about how what we eat affects our health.

Journal Reference

Hall, K. D., Guo, J., Courville, A. B., Boring, J., Brychta, R., Chen, K. Y., Darcey, V., Forde, C. G., Gharib, A. M., Gallagher, I., Howard, R., Joseph, P. V., Milley, L., Ouwerkerk, R., Raisinger, K., Rozga, I., Schick, A., Stagliano, M., Torres, S., … Chung, S. T. (2021). Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nature Medicine, 27(2), 344–353. https://doi.org/10.1038/s41591-020-01209-1 

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