Keto vs. low-fat diets: which is more sustainable in the long term?

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLMMay 24 2023

In a recent study published in the Journal of Food Science and Nutrition Research, researchers investigated whether commercial weight loss diets meet the recommended dietary requirements for essential nutrients and are suitable for long-term use.

Study: High Carbohydrate vs High Fat Diets: Which is Preferable for Long-term Use? Image Credit: nadianb/Shutterstock.com

Background

Research indicates that commercially manufactured weight loss diets are effective in weight reduction, and a few also reduce the risk of several chronic diseases.

However, their nutrient composition varies significantly across the type and percentage of essential nutrients such as fats, proteins, and carbohydrates, as well as the micronutrient composition.

While some diets comprise high carbohydrate and low-fat content, others, such as the ketogenic diet, aim at a high fat and low carbohydrate content. However, while almost all of these diets have successfully reduced weight in the short term, whether these diets provide all the essential nutrients necessary for sustained use remains unclear.

About the study

In the present study, the researchers selected two established commercially formulated weight loss diets — a high carbohydrate and low-fat diet and a high-fat and low carbohydrate diet — and used the suggested meal plans of these diets to assess their nutritional content adequacy.

The software Nutrition Data System for Research (NDSR) was used for the dietary analysis. While the software reported the 174 nutrients, their ratios, and other related components, it did not report biologically active components such as plant phytochemicals, sugar alcohols, polyols, non-essential nutrients, or essential amino acids with no standard recommendations.

Only nutrients with recommended dietary allowances (RDA) and dietary reference index (DRI) were reported. In total, 62 nutrient entries were written.

Five menus were selected randomly from the manuals for the commercial diet, and the menus contained details on the portion sizes and ingredients for all three meals of the day and snacks.

Diet 1 had a high carbohydrate content with plant-based protein and low-fat content, while Diet 2 had a low carbohydrate content with high fat and moderate protein.

Results

The results indicated that Diet 1, which had high carbohydrate and low-fat content, satisfied 81% (50 out of 62) of the nutrient requirements but did not provide the recommended levels of vitamins D and B12 and essential fatty acids. However, the glycemic load and fiber content was higher than the suggested levels.

Diet 2, which was high in fats and low in carbohydrates, met 71% (46 out of 62) of the essential nutrient requirements but was excessively high in the percentage of sodium, saturated fat, and cholesterol.

Furthermore, the low carbohydrate content of Diet 2 resulted in a sub-optimal fiber and vitamin B-complex intake, including total folate, niacin, and B1.

Diet 1, referred to as "heart friendly" by the manufacturer, incorporates nutrients essential for optimal cardiovascular function, such as high fiber and low sodium, cholesterol, saturated fat, and sugar.

The low vitamin B12  levels could be explained by the insufficient animal protein portions in Diet 1 since vitamin B12 is only generated in animals. In contrast, the low vitamin D levels could be due to the low dairy content of Diet 1.

The low-fat content of Diet 1 also resulted in low eicosapentaenoic acid and docosahexaenoic acid levels.

Diet 2, which was referred to as the "fat burning" diet due to the high fat and shallow carbohydrate content, aims to stimulate ketone body formation by mobilizing lipid stores and is also believed to have other therapeutic effects such as lowering the risk of type 2 diabetes and insulin resistance.

The low carbohydrate content of Diet 2 resulted in a decrease in vitamin B complex and fiber levels.

Furthermore, since the ketogenic diet also results in water loss from the body due to the low carbohydrate content, it requires a higher intake of water and electrolytes.

While the low levels of essential fatty acids and fat-soluble vitamins in uncharacteristic of a high-fat diet, the researchers believe that this could be explained by the omission of seafood in the five randomly selected diets.

One of the study's strengths is the use of exact portion sizes and ingredients from the recipe books published by the manufacturers, and the use of the NDSR software allowed the researchers to conduct an extensive analysis of the commercial diets available for weight loss.

The authors believe that the findings suggested that neither the high-carbohydrate nor the high-fat diet is sustainable as both decrease some essential nutrients.

Conclusions

Overall, the findings indicated that none of the tested commercial diets for weight loss provided all the essential nutrients at the recommended levels.

While some might be successful in the short term in reducing weight, long-term adherence to these diets will result in deficiencies of essential nutrients. Therefore, the researchers recommend that neither of these diets be used in the long term.