Low carb, keto and Mediterranean diets compared

For comparison: a balanced diet in Cochrane's terms has 45 to 65% carbohydrates.^[2] The DGE names more than 50% for a wholesome mixed diet.^[5]

The difference is small. In a Cochrane review of 61 studies, low carb probably made little or no difference compared with balanced diets after one to two years, about 0.9 kg in people without diabetes.^[2]

In a large study of 609 adults, low fat and low carb were 0.7 kg apart after one year, and neither genes nor insulin predicted who did better on what.^[6] An analysis of 121 studies saw similar losses at 6 months, and at 12 months they shrank for all diets.^[7]

Whatever the diet, the S3 guideline expects an average of about 5 to 6 kg after 12 months with a deficit of 500 to 600 kcal a day.^[1]

In a study of 160 people, weight loss depended on how well someone stuck with it, not on the diet.^[8] These are links, and people who lose weight may also find it easier to stick with it.

So it pays to ask honestly: could I still eat like this in a year, with family, canteen and holidays? A diet you drop after three weeks does little.

The Mediterranean diet has the most data on the heart and mortality. The well-known PREDIMED study of 7,447 people was retracted in 2018 because of flaws in allocation and reanalysed. About 30% fewer major cardiovascular events remained.^[9] In an analysis of 40 studies, Mediterranean and low-fat programmes lowered mortality, with no convincing difference between them.^[10] Cochrane is more cautious and sees uncertainty on hard outcomes.^[4]

Such studies are missing for low carb and keto. Observational data show that the source matters: when carbohydrates were replaced by animal fat and protein the risk of death was higher, with plant sources it was lower.^[11] The WHO names no amount of carbohydrates and relies on whole grains, vegetables, fruit and pulses instead.^[12]

On keto, LDL cholesterol can rise. In a small comparison of 33 people it rose by 10% on keto and fell by 5% on a Mediterranean diet.^[13] Have your blood lipids checked if you eat this way for longer.

• Diabetes medicines: With SGLT2 inhibitors, case reports describe a dangerous acidosis after a short time. The product information warns in general about conditions with restricted food intake.^[14][15]
• Insulin and type 1 diabetes: According to the German Diabetes Society this needs close monitoring.^[16]
• Pregnancy and breastfeeding: Experts currently advise against it, and the data are thin.^[3][17]
• Kidneys and liver: Keto counts as delicate with advanced disease.^[18]

If you take medicines or have a health condition, talk to your doctor first. The S3 guideline advises against one-sided extreme diets.^[1] More under When to get medical advice.