Apple cider vinegar is a traditional folk remedy that has been around for many centuries. But is it beneficial for our health, asks Michael Mosley.
Cider vinegar is made by mixing chopped-up apples with water and sugar, then allowing the mixture to ferment, turning some of it into acetic acid.
Despite being acidic and definitely something of an acquired taste, in recent years cider vinegar has become incredibly popular. At least a part of that is because of claims that it can help with everything from obesity to split ends and arthritis.
But which, if any, of the many different health claims made on its behalf stand up to scientific scrutiny? For Trust Me, I'm A Doctor we teamed up with Dr James Brown from Aston University to find out.
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Michael Mosley (left, above, with Dr James Brown) presents Trust Me, I'm A Doctor which returns for a new series on Thursday 1 September on BBC Two at 20:00 BST - catch up on BBC iPlayer
We started by testing a claim which does seem to have the most scientific credibility - the claim that drinking a couple of tablespoons of vinegar, diluted in water, before a meal will help you control your blood sugar levels.
To see if there was substance to this idea we recruited healthy volunteers and asked them to eat two bagels, after having fasted overnight. We measured their blood sugar levels before and after eating and, as we expected, bagel consumption was followed by a large and rapid rise in their blood sugar levels.
The next day we asked them to consume another two bagels, but this time we asked them to knock back a diluted shot of apple cider vinegar just before doing so. Finally, we repeated the test a few days later, but this time we got our brave volunteers to gulp down some dilute malt vinegar before the bagel.
It turned out that the cider vinegar, but not the malt vinegar, had a big impact, reducing the amount of sugar in the volunteers' blood by 36% over 90 minutes.
This could be because the acetic acid in the cider vinegar suppresses the breakdown of starches, which means that if you consume it before a carb-rich meal, less sugar will get absorbed. We expected the malt vinegar to have a similar effect to the cider vinegar, but in our small study it didn't.
Next, we wanted to see whether cider vinegar lived up to claims that it helps with weight loss, lowers cholesterol and reduces inflammation (which might help with conditions like rheumatoid/inflammatory arthritis and eczema).
We recruited 30 volunteers and divided them into three groups. Our first group were asked to drink two tablespoons of cider vinegar diluted in 200ml of water twice a day, every day, before a meal. The second group were asked to do the same with malt vinegar and the final group were given a placebo consisting of coloured water.
Two months later I met up with Dr Brown and our volunteers to find out how they had all got on. Most were very positive about the experience. A few thought they might have lost a bit of weight, with one saying she didn't feel as much craving for sweet things. Another volunteer with mild arthritis told me: "I have had less aches and pains in my joints, especially after exercise." Yet another thought it had improved her eczema.
But what did Dr Brown's tests reveal?
"I'm sorry to say," he told his expectant audience, "that none of you lost any weight."
That was disappointing, though not entirely surprising.
So what about the alleged anti-inflammatory properties of vinegar, which could explain improvements in arthritis or eczema? As part of the testing Dr Brown had measured our volunteers' blood levels of something called C-reactive protein (CRP), a marker for inflammation in the body.
Again, unfortunately, we didn't see any changes. We did see a small fall in the CRP levels of some of those taking cider vinegar, but it wasn't enough to get excited about.
So far things had been rather disappointing for vinegar guzzlers. Dr Brown, however, had the results for one final test to reveal - the effect on blood fats.
In neither the placebo nor the malt vinegar group was there any change. But those consuming cider vinegar saw an average 13% reduction in total cholesterol, with a strikingly large reduction in triglycerides (a form of fat). And this was a particularly impressive finding because our volunteers were all healthy at the start, with normal cholesterol levels.
"Bringing cholesterol levels down like this", Dr Brown told me, "can significantly reduce your chances of having a heart attack in the future. So we were really excited to see that finding."
So cider vinegar probably won't help anyone slim down, but it may help those who struggle with their blood sugar or cholesterol levels. Because it is acidic I would only drink it diluted or use it sparingly in food.
Michael Mosley presents a new series of "Trust Me I'm a Doctor" which starts on BBC Two on Thursday 1 September at 20:00 BST