Does eating a lot of sugar give you type 2 diabetes?

Sugary drinks are the most well-supported source of sugar when it comes to type 2 diabetes. A meta-analysis of eight large population studies involving more than 310,000 participants found that people who drink one to two glasses of soft drinks, energy drinks or fruit drinks per day have a 25 to 26 percent higher risk of type 2 diabetes compared with people who rarely or never do so. Fruit juice also scores unfavourably: each additional serving per day is associated with five percent more risk. This association has been found in multiple independent studies and is statistically robust, although these are population studies and not a direct test of causality.

Sugar from solid food behaves differently from sugar in drinks. A large-scale analysis shows that eating more sugar through ordinary food, that is, not through drinks, is not associated with more diabetes. For added sugar and fructose consumed through food, no association was found at all. At 20 grams of extra sugar per day through food, the risk was even slightly lower. The quality of evidence for this component is low to moderate, but the message is consistent: the form in which sugar is consumed matters. Liquid sugar appears to be more harmful than sugar in solid food, presumably because drinks regulate satiety less effectively and the sugar enters the bloodstream more quickly.

Early exposure to sugar may also play a role over the long term. A historical study of British sugar rationing after the Second World War shows that people who received little sugar in the womb and as infants had roughly 35 percent less chance of developing type 2 diabetes later in life, and that the disease began on average four years later. One third of that protective effect came from rationing during pregnancy alone. This is a so-called natural experiment, not a classic randomised study, but the outcome points to a possible causal relationship in the early stages of life.

Excess weight and physical inactivity are the most strongly proven, reversible risk factors for type 2 diabetes. In a randomised study involving 3,234 participants at elevated risk, a lifestyle programme aimed at seven percent weight loss and 150 minutes of physical activity per week reduced the risk by 58 percent. That is stronger than the effect of medication (metformin, which reduced the risk by 31 percent in the same study). Sugar consumption contributes to excess weight, but the extra kilograms themselves and the lack of physical activity are the biggest levers.

Besides sugary drinks, processed meat and red meat are the food groups with the strongest evidence for an increased risk of type 2 diabetes. According to one large meta-analysis, people who consume a lot of these products in combination can even triple their risk compared with people who rarely eat them. For people who want to reduce their risk, it is therefore worthwhile to look simultaneously at drinks, processed meats and body weight.

For people who already have type 2 diabetes or prediabetes: a ketogenic diet (extremely low in carbohydrates) improves blood sugar levels after twelve weeks just as well as a Mediterranean diet, but has the drawback that LDL cholesterol rises (an unfavourable cardiovascular factor) and that it is harder to maintain. The Mediterranean diet scores comparably on blood sugar without that side effect, which in practice makes it a better choice for a sustainable approach.