Does wine break a fast?

A 150 ml (5 fl oz) glass of red wine has about 125 kcal. A standard 175 ml glass of 12% wine has up to about 158 kcal. Alcohol carries about 7 kcal per gram. That 175 ml glass holds about 17 g of alcohol, which is about 116 kcal on its own. So most of the calories in a glass of dry wine are the alcohol itself.

On the four goals this site uses to sort answers, wine breaks a fast for weight loss, autophagy and gut rest. One glass is well over twice the common 50-calorie rule of thumb, which is not an official limit. Your body has to absorb and process every glass, so autophagy and gut rest are broken too. Alcohol also slows fat burning after the drink. One study gave 8 men 24 g of alcohol, about one and a half 175 ml glasses of 12% wine. Their fat burning fell by 73% for some hours. The study was small, so the evidence is early.

Blood sugar is a grey area. Alcohol never gets a safe verdict on this site. Dry wine has less sugar than sweet and dessert wines, so its calories come mostly from the alcohol. Alcohol can push blood sugar too low in people who take insulin or some other diabetes medicines, especially when they drink without food. If that applies to you, take your medicines as prescribed and ask your doctor how drinking fits with fasting.

Wine at the end of a fast, before you eat, hits harder. Food slows the absorption of alcohol and can lower the peak level in the body by about a third. If you drink, have the glass with a meal in your eating window. No amount of alcohol is free of risk. WHO Europe puts it this way, "No level of alcohol consumption is safe for our health."