Q. Is it true that vinegar makes a meal low in GI?

A. Yes. Adding a tablespoon of vinegar to a meal (such as the vinegar in your salad dressing) has long been known to lower the body's blood glucose response to the meal by up to 30 per cent.

The theory is that adding vinegar to a meal slows down the rate at which food empties from the stomach and enters the small intestine for digestion, therefore slowing the absorption of glucose into the blood.

Does it work with all types of vinegar? Yes as far as we know. It's the acidity from the acetic acid that's responsible and the resultant low pH is thought to slow stomach emptying. So balsamic, wine or raspberry vinegar all work the same way.

And you get the same effect from any acidic food like lemon juice or acidic fruits (grapefruit, kiwi fruit) or pickled vegetables (pickled gherkins, pickled onions) which can slow down stomach emptying.

A 2010 research paper reported that the vinegar effect is more pronounced after a high GI meal and not the low GI meals nutritionists suggest for good health. So if you're already choosing legumes, grainy breads and pasta you may not notice as much of an effect. But if you choose high GI foods (e.g. potatoes),  you may notice an effect.

• Read more about the GI at the Glycemic Index website.

The bottom line

 Vinegar reduces high blood glucose in patients with type 2 diabetes when added to a high, but not to a low, Glycaemic Index meal.