Published in Cell reports medicineThe Center for Nutrition, Exercise, and Metabolism study involved 53 healthy adults for up to 12 weeks. Participants followed a moderate sugar diet (control), a low-sugar diet (less than 5% of calories from sugar) or a ketogenic (keto) low-carb diet (less than 8% of calories from carbohydrates).
Key findings include:
- Increased cholesterol: The keto diet increased cholesterol levels, especially in small and medium LDL particles. The diet increased apolipoprotein B (apoB), which causes plaque buildup in the arteries. In contrast, the low-sugar diet significantly reduced cholesterol levels in LDL particles.
- Reduced beneficial gut bacteria: The keto diet changed the composition of the gut microbiome, specifically decreasing Bifidobacteria, beneficial bacteria often found in probiotics. This bacterium has various benefits: producing B vitamins, inhibiting pathogens and harmful bacteria and lowering cholesterol. Sugar restriction had no significant impact on the composition of the gut microbiome.
- Glucose tolerance: The keto diet reduced glucose tolerance, meaning adults’ bodies became less efficient at processing carbohydrates.
- Both diets resulted in fat loss: The Keto diet resulted in an average of 2.9 kg of fat mass loss per person, while the sugar-restricted diet followed with an average of 2.1 kg of fat mass loss per person after 12 weeks.
- Metabolism: Researchers also noticed that the keto diet caused significant changes in lipid metabolism and muscle energy expenditure, shifting the body’s fuel preference from glucose to fats.
- Physical activity levels: Both sugar restriction and keto diets achieved fat loss without changing physical activity levels. Previous studies from the Center for Nutrition, Exercise and Metabolism have shown that skipping breakfast or intermittent fasting causes a reduction in physical activity.
Lead researcher Dr. Aaron Hengist highlighted the cholesterol findings in question:
“Despite the reduction in fat mass, the ketogenic diet increased the levels of unfavorable fats in the blood of our participants, which, if continued for years, could have long-term health consequences such as an increased risk of heart disease and strokes.”
Dr. Russell Davies, who led the microbiome research, explained the impact on gut health:
“Dietary fiber is essential for the survival of beneficial intestinal bacteria such as Bifidobacteria. The ketogenic diet reduced fiber intake to around 15 grams per day, half the NHS recommended intake. This reduction in Bifidobacteria could contribute to significant long-term health consequences, such as increased risk of digestive disorders such as irritable bowel disease, increased risk of intestinal infections and weakened immune function.”
Professor Javier Gonzalez, who oversaw the research, commented on the glucose findings:
“The ketogenic diet lowered fasting glucose levels, but also reduced the body’s ability to process carbohydrates from a meal. By measuring protein in muscle samples taken from participants’ legs, we think this is likely an adaptive response to eating fewer carbohydrates every day. and reflects insulin resistance to carbohydrate storage in the muscles. This insulin resistance isn’t necessarily a bad thing when people follow a ketogenic diet, but if these changes persist when people return to a high-carb diet, it can increase the risk of developing type 2. diabetes in the long term”
In light of this new research, the academics conclude that if you are considering dieting, a low-sugar diet will be better for most people. More work is needed to understand how individuals can benefit from each type of diet. The government recommends that free sugars (those added to food or drink or naturally occurring in honey, syrups, fruit juices and smoothies) should be limited to less than 5% of total energy intake. Professor Dylan Thompson, who also supervised the work, said:
“The ketogenic diet is effective for fat loss, but it has varied metabolic and microbiome effects that may not be suitable for everyone. Sugar restriction, on the other hand, supports government guidelines for reducing free sugar intake, promoting fat loss without apparent negative health consequences.”
This work was supported by an initial grant from The Rank Prize Funds, followed by funding from the Cosun Nutrition Centre, the University of Bath and Ian Tarr. Exploratory analyzes include fellowship support for some researchers from the British Heart Foundation and the Medical Research Council.
