A study found that ketogenic low-carbohydrate diets can raise cholesterol levels while decreasing beneficial gut bacteria, notably Bifidobacterium. The Centre for Nutrition, Exercise, and Metabolism conducted a 12-week study on 53 healthy people, which was published in Cell Reports Medicine. Participants chose between a moderate sugar diet (control), a low-sugar diet (less than 5% of calories from sugar), and a ketogenic (keto) low-carbohydrate diet (less than 8% of calories from carbohydrates).
Key findings include:
- Increased Cholesterol: The keto diet improved cholesterol levels, especially in tiny and medium-sized LDL particles. The diet raised apolipoprotein B (apoB), which leads to plaque development in arteries. In contrast, a low-sugar diet considerably lowered cholesterol levels in LDL particles.
- Reduced Favourable Gut Bacteria: The keto diet reduced beneficial gut bacteria, particularly Bifidobacteria, which are commonly found in probiotics. This bacteria has numerous benefits, including the production of B vitamins, the inhibition of infections and dangerous bacteria, and the reduction of cholesterol. Sugar restriction had no substantial impact on the gut microbiota makeup.
- Glucose Tolerance: The keto diet reduced glucose tolerance, meaning the adults’ bodies became less efficient at handling carbohydrates.
- Both Diets Resulted In Fat Loss: Keto Diet resulted in an average of 2.9 kg fat mass loss per person, whilst the sugar restricted diet followed with an average 2.1 kg fat mass loss per person at 12 weeks.
- Metabolism: Researchers also noticed that the keto diet caused significant changes in lipid metabolism and muscle energy use, 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 Centre for Nutrition, Exercise and Metabolism have shown that skipping breakfast or intermittent fasting cause reductions in physical activity.
Despite reducing fat mass, the ketogenic diet increased the levels of unfavourable fats in the blood of our participants, which, if sustained over years, could have long-term health implications such as increased risk of heart disease and stroke.
Dr. Aaron Hengist
Lead researcher Dr. Aaron Hengist highlighted the concerning cholesterol findings:
“Despite reducing fat mass, the ketogenic diet increased the levels of unfavorable fats in the blood of our participants, which, if sustained over the years, could have long-term health implications such as increased risk of heart disease and stroke.”
Dr. Russell Davies, who led the microbiome research, explained the impact on gut health:
“Dietary fiber is essential for the survival of beneficial gut bacteria like Bifidobacteria. The ketogenic diet reduced fiber intake to around 15 grams per day, half the NHS-recommended intake. This reduction in Bifidobacteria might contribute to significant long-term health consequences such as an increased risk of digestive disorders like irritable bowel disease, increased risk of intestinal infection and a weakened immune function.”
Professor Javier Gonzalez, who oversaw the research, commented on the glucose findings:
“The ketogenic diet reduced fasting glucose levels but also reduced the body’s ability to handle carbs from a meal. By measuring proteins in muscle samples taken from participants’ legs, we think this is probably an adaptive response to eating less carbohydrates day-to-day and reflects insulin resistance to storing carbs in muscle. This insulin resistance is not necessarily a bad thing if people are following a ketogenic diet, but if these changes persist when people switch back to a higher carbohydrate diet it could increase the risk of developing type 2 diabetes in the long-term”
In light of this new research, scientists conclude that most people will benefit from a low-sugar diet. More research is needed to determine how people can benefit from each type of diet. The government recommends that free sugars (those added to food or drink or found naturally in honey, syrups, fruit juices, and smoothies) be kept to less than 5% of total caloric intake.
Professor Dylan Thompson, who oversaw the study, stated that while the ketogenic diet is helpful for fat loss, it may not be suitable for all individuals due to its diverse metabolic and microbial impacts. Sugar restriction, on the other hand, supports government standards for lowering free sugar intake, increasing fat loss while having no evident negative health consequences.
