Did you know mushrooms produce Vitamin D even after they've been picked? Professor Alice Roberts reveals some of the fascinating facts she uncovered for new programme Britain's Favourite Foods

After a long session pounding the treadmill in the gym, what do you tend to reach for to refresh yourself? The chances are, it's probably water or a sports drink. But a new BBC show reveals that you'd be better off pouring yourself a glass of milk.

For Britain's Favourite Foods: Are They Good For You?, which aired on April 14, Professor Alice Roberts immersed herself in some of the most fascinating recent scientific research about the country's most popular foods. Here, she shares some of the facts she uncovered.

Milk is the ultimate gym drink

To prove that milk is one of the most effective drinks to rehydrate with, Professor Roberts recruited a team of student volunteers from the University of Birmingham to exercise with her, "then rehydrate with three different drinksmilk, water and a sports drink. Milk stayed in the system for much longer than water or the sports drink".

The reason, she explains, is because milk releases very slowly into the small intestine, so it is absorbed much more gradually into the bloodstream, helping the body retain fluid for longer. It also has a high number of electrolytes, including sodium and potassium, which are lost from the body when sweating.

Dairy doesn't make you fat

Milk's superpowers go beyond simply rehdyrating you after a tough work-out, however. Another revelation featured in the programme is that although many people associate large quantities of dairy with putting on weight, research from the University of Copenhagen shows that in cultures with high-dairy diets, people actually aren't as heavy as might be imagined.

"We found a lovely contributor, Carol, who ate a high-dairy diet for two weeks and a low-dairy diet for two weeks. We asked her to collect her poo, which we sent to Copenhagen so the scientists could analyse it," says Professor Roberts.

The Danish team's analysis of the faeces backed up what their previous research had suggested"that people with a high-dairy diet have a lot more fat passing through at the other end". Carol lost fifty per cent more fat through her stools when on the high-dairy diet. The scientists believe this could be the calcium in dairy food combines with fat to create a "soap-like substance" which slides through the body without being absorbed.

Of course, this doesn't mean you can binge on ice cream. "We're not suggesting that you can eat a huge quantity of dairy and lose weight, but we can maybe feel a bit less guilty when eating cheese," says Professor Roberts.

Mushrooms can boost your vitamin D

We all know that oily fish and eggs are a good source of Vitamin Dbut did you know that mushrooms can be too?

According to Dr Roberts, wild mushrooms that have been exposed to sunlight "make their own Vitamin D just like humans do".

"Most mushrooms we buy in the supermarket are grown in the dark so have negligible levels of Vitamin D. But even after being picked, if you expose mushrooms to sunlight, they will start manufacturing it," she explains.

Supermarkets have apparently already shown interest in the researchso you can probably expect Vitamin D-boosting mushrooms in your local Tesco soon.