Is intermittent fasting safe if you have type 2 diabetes?
Intermittent fasting can be safe in type 2 diabetes, but only if you do this in consultation with your doctor, because your medication will almost always need to be adjusted to prevent blood sugar from dropping too low.
Intermittent fasting lowers average blood sugar levels in people with type 2 diabetes. The reduction is modest but clinically meaningful: depending on the study, it amounts to an improvement of 0.3 to 0.9 percentage points on the HbA1c measure (a marker of blood sugar control over the preceding months). That effect is comparable to a standard calorie-restricted diet, but intermittent fasting is not clearly superior in this regard. Weight loss also occurs, on average somewhere between 1.7 and nearly 7 kg depending on the study and its duration. Blood pressure and LDL cholesterol also fall, although the precise amounts for blood pressure and cholesterol cannot be reliably extracted from the available data.
The greatest safety risk is blood sugar dropping too low, in other words a hypoglycaemic episode. This risk applies in particular if you inject insulin or take certain blood-sugar-lowering medications, such as glibenclamide or gliclazide. In studies where doctors adjusted medication in good time and participants measured their blood sugar regularly, no serious hypoglycaemic episodes occurred. However, in the first weeks of fasting, before medication had been properly adjusted, 35% of participants taking insulin or these tablets experienced a hypoglycaemic or hyperglycaemic episode in one of the studies. That is comparable to the control group, but it does show that the initial period requires extra attention.
Intermittent fasting is therefore not something to start on your own if you have type 2 diabetes. All studies emphasise that medication must be adjusted before or at the start of fasting, and that blood sugar must be monitored regularly. If you do this in consultation with your doctor or diabetes nurse, the risk of serious adverse events appears manageable.
Time-restricted eating, a variant in which you eat only within a fixed daily window of, for example, ten hours, appears easier to sustain than individual dietary advice. In an Australian study, participants adhered to their eating window on an average of six out of seven days, and self-reported adherence was significantly higher than in the dietary advice group.
What we do not yet know is how safe and effective intermittent fasting is in the long term. Most studies lasted only twelve weeks to six months, and large long-term studies are still lacking. It is therefore too early for firm conclusions about which exact form of fasting works best, or about effects after years.
This answer is based on several randomised studies, two large systematic reviews with meta-analyses (the largest of which pooled data from 5,369 patients), a smaller meta-analysis of four studies, and a review article. The findings on blood sugar control and weight are reasonably consistent. The evidence on long-term safety is thin: most studies lasted no more than six months and had small sample sizes. The researchers themselves identify the short duration and small numbers as limitations.
Does eating a lot of sugar give you type 2 diabetes?
Sugary drinks clearly and demonstrably raise your risk of type 2 diabetes. Sugar from solid food barely does. The biggest difference comes from drinking fewer sugary drinks, moving more, and losing weight.
Does coffee help prevent type 2 diabetes?
Large population research shows that regular coffee drinkers develop type 2 diabetes considerably less often, but whether coffee itself is the cause remains uncertain.
What does intermittent fasting do to your insulin sensitivity?
Intermittent fasting improves insulin sensitivity in most people, but watch out for possible muscle loss and hormonal effects, especially if you combine it with intensive exercise.
Does it make sense to limit blood sugar spikes, even without diabetes?
Limiting blood sugar spikes makes sense even without diabetes: the risk of cardiovascular disease appears to rise with spikes that are still officially considered 'normal', and walking immediately after a meal is a simple, evidence-based way to reduce those spikes.
Is intermittent fasting safe during pregnancy?
For healthy pregnant women, fasting does not appear to increase major risks such as preterm birth or low birth weight, but fatigue and dehydration are real complaints. If you have diabetes or are early in your pregnancy, discuss fasting with your doctor first.
Is intermittent fasting worth it?
Intermittent fasting aids weight loss and also shows improvements in body fat, waist circumference, and certain blood markers. It works about as well as other diets where you eat the same number of calories.