The "low-carb versus low-fat" debate has run for decades. Large trials now give a fairly clear answer.

Weight loss

When calories and protein are matched, low-carb and low-fat diets produce similar fat loss. In a large year-long trial comparing healthy low-fat and healthy low-carb diets, average weight loss was similar between groups, with big individual variation in both.

Early "quick wins" on keto

Ketogenic diets often produce rapid weight loss in the first week or two. Much of this is water: cutting carbs depletes glycogen, which is stored with water.

Appetite

Some people find keto reduces hunger; others find it restrictive. Low-fat, high-volume eating suits people who like big portions.

Health markers

• Low-carb diets can improve blood sugar control and triglycerides for some people.
• Very high saturated fat intake on keto can raise LDL cholesterol in some people.
• Both approaches work best when based on minimally processed foods.

Performance

Keto tends to impair high-intensity and sprint performance, which relies on carbohydrates.

The verdict

The best diet is the one you can sustain while getting enough protein, fibre and micronutrients. If you have diabetes or take medication, speak to your doctor before starting a ketogenic diet.