Does High Blood Sugar Cause Weight Gain? The Insulin Link

Why do two people eating identical calories end up with different weight outcomes?

Their post-meal blood-sugar response. The carbohydrate-insulin model predicts that the same person could do differently on a meal of chicken and avocado than on a pasta and whole-wheat toast meal with the same calories, although calorie-matched trials find smaller differences than that. Calories report intake; blood sugar response is a useful second number.

How does blood sugar drive weight gain?

According to the carbohydrate-insulin model, blood sugar can influence weight gain through a six-step sequence in which a blood sugar spike calls in a lot of insulin, and high insulin slows the release of stored fat, so fat is more likely stored than burned. We argue it is a useful second number beside calories. Dr. Benjamin Bikman, professor of cell biology at BYU, has argued that chronic hyperinsulinemia, rather than intake alone, is a primary driver of fat accumulation:

1. You eat a high-carbohydrate food. The carbohydrates begin breaking down into simple sugars as you digest.
2. Blood sugar rises rapidly. Those simple sugars enter your bloodstream.
3. The pancreas intervenes. The body calls in insulin to move the sugar out of the blood and into cells.
4. High insulin slows the release of stored fat. While insulin is high, the release of stored fat slows (Jensen et al., Diabetes 1989), so fat is more likely stored than burned.
5. Blood sugar may dip. In some people a large insulin response is followed by a fairly quick fall in blood sugar.
6. Hunger may return. The model links that dip to feeling hungry again sooner, and the cycle can repeat. Hunger has many causes, so this is a proposed pattern, not a rule.

Eating protein and healthy fats tends to produce a smaller blood sugar rise and a smaller insulin response, which is the pattern the carbohydrate-insulin model links to fat being more likely burned than stored. When the spike-and-surge cycle repeats for years, cells may become less responsive to insulin, which is insulin resistance.

Which everyday foods cause the biggest blood sugar spikes?

Sweet drinks and pure sugar tend to cause the biggest spikes, followed by refined carbohydrates with no structural fibre to slow them down, and some of the worst offenders are surprising. For specific examples, see how 23 common foods score on the Weight Impact Score.

This is why "healthy" low-fat flavoured yogurt, fruit juice, oat milk, and whole-wheat bread are repeat offenders for blood sugar spikes. They carry the health halo but can still raise blood sugar quickly. Jessie Inchauspé reports in her blood sugar curve work that eating a small protein portion before carbohydrates can flatten the subsequent blood sugar spike. Eating protein and vegetables first may change how much insulin the meal calls for. For a breakfast built that way, see low insulin breakfast foods.

Ready to stop guessing what to eat?

Do you need a blood sugar sensor to see how a meal affects you?

No. A wearable blood sugar sensor (CGM) is the most direct way to see your own response to a specific plate of food, but it takes a sensor with a small needle in the back of the arm, and an estimate is enough for everyday choices.

RealFoods, an iPhone app, estimates a meal's likely blood sugar and insulin impact from a photo, text or barcode and shows it as the Weight Impact Score. We argue this trade, slightly less precision than a continuous monitor in exchange for friction-free, every-meal feedback, is the right one for the many people who will never wear a sensor. See how RealFoods works for the scan in action.

Common questions

Can blood sugar cause weight gain even when calories are the same?

Possibly, according to the carbohydrate-insulin model, which is debated: repeated post-meal blood sugar spikes raise insulin, and high insulin slows lipolysis, the release of stored fat (Jensen et al., Diabetes 1989). Calorie-matched trials find smaller differences than the model predicts (for example Hall et al., Cell Metabolism 2015, 19 adults with obesity in a metabolic ward). In the 2015 Cell study by Zeevi and colleagues, which tracked 800 people with sensors that track blood sugar continuously, identical meals produced highly variable blood sugar responses between individuals, so the same calorie total does not give everyone the same blood sugar curve.

Which foods spike blood sugar the most?

Sugar-sweetened beverages and fibre-stripped refined carbohydrates tend to produce the largest blood sugar rises. Fruit juices, flavoured low-fat yogurts, oat milk, and refined breads are common examples.

How can I blunt a blood sugar spike?

Choose less-refined carbohydrate and eat it with protein and fibre. Protein slows gastric emptying and fibre physically slows the absorption of sugar. Order helps too: in a crossover trial of 16 adults with type 2 diabetes, eating protein and vegetables before carbohydrate lowered the post-meal blood sugar peak by 54% compared with eating carbohydrate first (Shukla et al., BMJ Open Diabetes Research & Care 2017).

Want to know more? Read up on how the Weight Impact Score works, see the full list of foods that cause weight gain, and understand the core issue with conventional calorie counting.