Cutting carbs to lose weight has become a national pastime, and the ketogenic diet is the latest star of the show. It promises a metabolic magic trick: transform your body into a fat-burning machine by ditching almost all carbohydrates. But a new study from researchers at the University of Bath suggests that while the keto diet is great for shedding fat, it may also come with a handful of unwelcome consequences that could do more harm than good.
Published in the journal Cell Reports Medicine, the study found that a low-sugar diet was a much safer path to weight loss than a ketogenic diet. Both groups lost a significant amount of fat, but only the keto diet caused concerning changes in the body’s metabolism and gut health. For anyone looking to lose weight and improve their health at the same time, this research offers a clear choice.
How the Study Worked
Researchers conducted a 12-week study with 53 healthy adults, placing them into one of three groups: a moderate-sugar “control” group, a low-sugar group, and a very low-carbohydrate ketogenic group. Participants followed these diets in their daily lives, with researchers tracking their progress through food diaries and regular check-ups. To confirm that the keto group was actually in a state of ketosis, researchers measured a specific byproduct in their urine. This “free-living” approach is important because it shows the results are more realistic and apply to everyday people.
A key part of the study was to see if the diets changed how much energy people burned, as it’s often theorized that cutting calories can make the body try to conserve energy by making people less active. The results proved this theory wrong. Neither diet caused any major changes in physical activity, which means the weight loss came directly from the participants consuming fewer calories, not from them burning more.
The Surprising Side Effects of Keto
While both diets led to fat loss, their effects on the body were very different. The ketogenic diet had a particularly concerning impact on the body’s ability to process sugar. The study found that the keto group had a temporary reduction in glucose tolerance, which means their bodies became less efficient at handling carbohydrates. This could be a precursor to developing type 2 diabetes in the long run. The low-sugar diet, by contrast, had no such effect.
The keto diet also increased levels of a protein known as apolipoprotein B (apoB). This protein is associated with the buildup of plaque in arteries, a major risk factor for heart disease. The low-sugar diet did the exact opposite, reducing harmful cholesterol and improving heart health markers.
Another major finding involved the gut microbiome—the trillions of microbes living in our digestive tract. The keto diet significantly reduced the amount of beneficial Bifidobacteria in the gut. These bacteria are crucial for a healthy digestive system and play a key role in producing vitamins and lowering cholesterol. The low-sugar diet, meanwhile, didn’t negatively impact the gut’s health at all.
Weighing the Options
It’s clear that a ketogenic diet is effective for fat loss, but this new research suggests it’s not without potential health trade-offs. The study’s lead researcher, Professor Dylan Thompson, noted that while keto is good for fat loss, it “comes with varied metabolic and microbiome effects that may not suit everyone.” The low-sugar diet, however, provided similar fat loss with none of these negative effects, and even improved some health markers.
The final takeaway is that when it comes to diets, quick results don’t always mean a healthier outcome. A low-sugar approach gives you a straightforward and safer path to the same goal: losing fat while also improving your overall health.
Paper Summary
Methodology
The study was a 12-week randomized controlled trial involving 53 healthy adults. Participants were split into three groups: a control group with a moderate sugar diet, a low-sugar diet group, and a ketogenic diet group. The study was conducted in a “free-living” environment, with researchers monitoring food intake and confirming adherence to the diets.
Results
Both the low-sugar and ketogenic diets resulted in fat loss. However, the ketogenic diet also increased lipoproteins linked to heart disease, reduced the body’s ability to process sugar, and altered the gut microbiome by decreasing beneficial Bifidobacteria. The low-sugar diet did not cause these negative effects and even improved some health markers.
Limitations
The study had a smaller sample size than planned due to dropouts. The high sugar intake of the control group may also limit the generalizability of the findings to a broader population.
Funding and Disclosures
The research received funding from The Rank Prize Funds, Cosun Nutrition Center, the University of Bath, and Ian Tarr. Exploratory analyses were supported by fellowships from the British Heart Foundation and the Medical Research Council.
Publication Information
The paper, titled “Ketogenic diet but not free-sugar restriction alters glucose tolerance, lipid metabolism, peripheral tissue phenotype, and gut microbiome: RCT,” was published in the journal Cell Reports Medicine on August 20, 2024.
