UK politician Tom Watson left a lot of people scratching their heads today when he revealed he has lost 45 kilograms and “reversed” his type 2 diabetes on a low-carb diet. Although it was coupled with an exercise regime, this is not supposed to be a healthy way to eat. What’s going on?

Watson’s impressive achievement cuts to the heart of the biggest controversy in nutrition science today. Mainstream medicine says diets should be low in fat and high in starchy carbohydrates such …