My gut reaction to veg is that it keeps you healthy – have you ever wondered they’re always so slim?

Have you ever wondered why vegetarians always seem to be on the slim side? Even though a lot of their food contains oil and their salads are laced with creamy dressings? Me too.

Well, it could be down to the way all those pulses, legumes and veggies keep their microbiome happy. You and I have a microbiome too. We all do.

It’s the bacterial population that inhabits our gut and it has many important functions, including strengthening our immune system and even controlling our appetite.

The microbiome is made up of hundreds of species of bacteria, good and bad.

If the good ones flourish, they keep the bad ones down, so we should do all we can to keep the good ones happy and healthy.

Vegetarians, simply by eating lots of veg, are doing that, particularly regarding one bacterium – prevotella.

And thereby hangs a tale. There’s mounting evidence that without certain bacteria, it’s impossible to lose weight.

The magic bacterium is prevotella, and according to a recent study, only half of us have it in sufficient numbers. No wonder diets don’t work for a lot of us.

The bacterium is thought to affect how we store fat and how we respond to hunger hormones. Prevotella flourishes if you eat a plant-based diet – lots of fruit, vegetables, leafy greens seeds, nuts, beans and lentils. Plus, you don’t eat very much meat.

The frustrating part is that prevotella can take months to populate the gut.

A study published earlier in the year revealed that dieters who follow a vegetarian eating plan lose nearly twice as much weight as low-calorie meat eaters.

Cutting out 500 calories a day and eating a plant-based diet results in an average weight loss of 13.67lbs (6.2kg) after six months, compared to 7.05lbs (3.2kg) in meat eaters.

Researchers believe this may be due to vegetarian diets encouraging prevotella – so changing our fat storage and insulin sensitivity, as well as giving us more energy, which helps us to stick to our eating plan.

Lead author Dr Hana Kahleova, from the Physicians Committee for Responsible Medicine in Washington DC, said: “A diet built around plants is naturally rich in fibre, vitamins, minerals and phytochemicals, which leaves us feeling energised and refreshed instead of hungry and fatigued.

“Part of the reason a vegetarian diet works so well for many people is because it’s easy to stick to.”

There’s a clear message here – eat more veg!