Keto and low-sugar diets work for weight loss
Researchers recruited 53 participants for a 12-week trial. The participants followed one of the following three diets.
- Moderate-sugar control diet – 50% carbs (20% of that sugars), 35% fats, 15% protein
- Low-sugar diet – 50% carbs (fewer than 5% of that sugars), 35% fats, 15% protein
- Keto diet – Fewer than 8% carbs, 77% fats, 15% protein
Both keto and low-sugar diets worked well. On average, they produced 2,9 kg and 2,1 kg of fat loss, respectively. Both achieved this fat loss without changing physical activity levels. However, the keto diet had several other effects on the participants that weren’t as favourable.
Higher cholesterol
The keto diet raised bad LDL cholesterol levels and apolipoprotein B, which causes plaque buildup in arteries. The low-sugar diet, on the other hand, reduced LDL cholesterol. This difference is crucial for those concerned about cardiovascular health.
“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,” said lead researcher Dr Aaron Hengist.
Fewer beneficial gut bacteria
The keto diet changed the gut microbiome composition, decreasing the quantity of beneficial Bifidobacteria. This type of bacteria produces B vitamins, inhibits pathogens and harmful bacteria, and lowers cholesterol. The low-sugar diet didn’t have a significant impact on the gut microbiome.
“Dietary fibre is essential for the survival of beneficial gut bacteria like Bifidobacteria. The ketogenic diet reduced fibre intake to around 15 grams per day, half the 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,” said co-author Dr Russell Davies.
Less efficient at handling carbs
The keto diet reduced glucose tolerance. This means that participants on this diet were less efficient at handling glucose after 12 weeks on keto. This is particularly concerning for those doing exercise at moderate to high intensity where the ability to utilise carbs is important for performance. On the other hand, the keto diet group improved their effectiveness in utilising fats for energy. This can be beneficial in ultra-endurance athletic events performed at low intensity.
Is keto a good choice?
This new study shows that there are downsides to going keto. It confirms that keto is an effective way to lose fat mass but people who are at a higher risk of cardiovascular disease or athletes who want to maximise carbohydrate utilisation should look for a different option.
“The ketogenic diet is effective for fat loss but comes with varied metabolic and microbiome effects that may not suit everyone. In contrast, sugar restriction supports government guidelines for reducing free sugar intake, promoting fat loss without apparent negative health impacts,” said co-author Prof Dylan Thompson.