Do high-carb diets cause type 2?
Type 2 diabetes develops due to defective insulin production and/or insulin resistance in cells. These changes can be detected in susceptible individuals even before blood glucose levels rise consistently — which means the physiological process changes first, not the glucose.
So it’s not carbs that cause type 2 diabetes, but rather it’s how susceptible your cells are to developing the condition that counts — and how factors like lifestyle, nutrition, and exercise influence that susceptibility.
What drives the development of Type 2 Diabetes?
Genetics play a very key role, but environmental and behavioural factors are critical too:
Excess calories, particularly stored as visceral or ectopic fat, can impair the function of organs such as the liver and pancreas.
Overweight or obesity (too many fat cells), especially without regular exercise, can drive systemic inflammation and interfere with insulin signalling — particularly from visceral fat around the liver and pancreas.
Low physical activity or a sedentary lifestyle reduces glucose metabolism and promotes liver fat accumulation.
Additional considerations:
Gut health: A healthy gut microbiome plays a role in reducing inflammation. Fibre is crucial here.
Fat quality: Replacing saturated fats with unsaturated fats may improve insulin sensitivity.
Fructose: It seems that very high liquid fructose intake can impair glucose and fat metabolism, promoting visceral fat storage around organs including the liver and pancreas.
Menopause: Hormonal changes can also increase the likelihood of central visceral fat gain.
Busting the myth: “Glucose causes insulin to rise, which causes insulin resistance.”
Insulin rises are a normal, healthy response to eating — not something to fear. In fact, extreme low-carb or ketogenic diets, while lowering glucose and insulin, can still result in insulin resistance over time due to high intakes of fat and low fibre leading to raised triglycerides, free fatty acids and cholesterol. These factors can increase inflammation and metabolic inefficiencies — leading us back to the same place: type 2.
What matters most for glucose metabolism is your environment: body fat stores, activity and exercise, and fibre intake — not whether or not you eat carbs.
Dr Nicola Guess sums it up perfectly:
“Nothing I can see suggests lowering glucose per se is protective against T2D, and - to reiterate - this is because T2D is caused by beta-cell dysfunction and insulin resistance - which themselves cause glucose to go up. And even if it did(!), limiting carbohydrate doesn’t even affect glucose levels because the body adapts to it…..unless you cut carbohydrate low enough to be ketogenic……… at which point the reduction in circulating glucose is replaced by an increase in circulating fat…….which itself causes insulin resistance..”
What about athletes consuming high carb gels including fructose?
Exercise is a particularly preventative factor when it comes to type 2. Even with a high carbohydrate diet, as seen in athletes, we don’t find an increased risk, even with fructose. Fructose is metabolised differently to glucose and evidence suggests in high amounts it can lead to impaired fat and glucose metabolism, but we are talking really high amounts of around 80g per day. One Torq or Lucozade energy gel contains approx 10g of fructose.
Endurance athletes may favour fructose to enhance glucose absorption, especially during performance, and so they may get close to 80g or even more, but with no evidence of extra risk.
If you’re not an athlete, unless you're consuming large volumes of sweetened drinks, you’re not likely to get anywhere near this amount.
The takeaway?
Exercise remains one of the most protective factors against Type 2 Diabetes, even in high-carb diets. But dietary quality still matters — for everyone, including athletes. Fibre intake, fat quality, and visceral fat stores all affect risk.
It’s not about cutting carbs - we need those for energy. It’s about improving the environment your body operates in to protect your cells and influence how they function.
