Ketogenic diets increase LDL cholesterol levels and reduce the amount of beneficial gut bacteria, which can increase the risk of developing cardiovascular disease in the long term.
A study from the University of Bath reveals that ketogenic diets characterized by being low in carbohydrates can increase cholesterol levels and reduce beneficial intestinal bacteria, specifically Bifidobacterium. Scientists from the University of Bristol, the Oxford University Hospital Trusts, Maastricht University and the Teagas Food Research Centre also participated in the research.
Researchers analyzed data from 53 healthy adults over a period of up to 12 weeks. Participants followed either a moderate-sugar diet (control), a low-sugar diet (less than 5% of calories from sugar), or a low-carb ketogenic or keto diet (less than 8% of calories from carbohydrates).
The findings have been published in Cell Reports Medicine and the main ones are:
- Increased cholesterol: The ketogenic diet raised cholesterol levels, especially in small and medium-sized LDL particles. It also increased apolipoprotein B (apoB), which contributes to plaque buildup in the arteries. In contrast, the low-sugar diet significantly reduced cholesterol in LDL particles.
- Reduction in beneficial gut bacteria: The ketogenic diet altered the composition of the gut microbiome, significantly decreasing Bifidobacteria, beneficial bacteria commonly found in probiotics. These bacteria have broad benefits, including producing B vitamins, inhibiting pathogens and harmful bacteria, and lowering cholesterol. Sugar restriction had no significant impact on gut microbiome composition.
- Glucose tolerance: The ketogenic diet reduced glucose tolerance, meaning the adults’ bodies became less efficient at handling carbohydrates.
- Fat loss: Both diets resulted in fat loss. The keto diet led to an average fat mass loss of 2.9 kg per person, while the sugar-restricted diet resulted in an average fat mass loss of 2.1 kg per person over 12 weeks.
- Metabolism: Researchers also noted that the ketogenic diet caused significant changes in lipid metabolism and muscle energy use, shifting the body’s fuel preference from glucose to fat.
- Physical activity levels: Both 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 lead to reductions in physical activity.
Increased risk of cardiovascular and digestive diseases
“Despite reducing fat mass, the ketogenic diet increased levels of unfavorable fats in the blood of our participants, something that, if sustained for years, could have long-term health implications, such as an increased risk of heart disease and stroke,” said lead researcher Dr. Aaron Hengist.
Dr Russell Davies, who led the microbiome research, explained the impact of these eating patterns on gut health: “Dietary fibre is essential for the survival of beneficial gut bacteria such as Bifidobacteria. The ketogenic diet reduced fibre 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 an increased risk of digestive disorders like inflammatory bowel disease, increased risk of gut infections and weakened immune function.”
“The ketogenic diet is effective for fat loss, but it carries varied metabolic and microbiological effects that may not be suitable for everyone.”
Professor Javier Gonzalez, who supervised the research, commented on the glucose-related findings: “The ketogenic diet reduced fasting glucose levels but also reduced the body’s ability to handle carbohydrate from a meal. By measuring protein in muscle samples taken from participants’ legs, we believe this is likely an adaptive response to eating less carbohydrate on a daily basis and reflects an insulin resistance to storing carbohydrate in muscle. This insulin resistance is not necessarily a bad thing if people are on a ketogenic diet, but if these changes persist when people return 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, the academics conclude that if you are considering dieting, a low-sugar diet will be best 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 foods or drinks or found naturally in honey, syrups, fruit juices and smoothies) should be restricted to less than 5% of total energy intake.
“The ketogenic diet is effective for fat loss, but carries varied metabolic and microbiological effects that may not be suitable for everyone. In contrast, sugar restriction supports government guidelines to reduce free sugar intake, promoting fat loss with no apparent negative impacts on health,” concludes Professor Dylan Thompson, who also supervised the work.
