By Kate Kelland

LONDON (Reuters) – People switching to a vegan diet – for January or for good – could reap health benefits such as weight loss and lower cholesterol, but should beware vegan junk food with little nutritional value, scientists are warning.

Plant-based food enthusiasts should also take supplements of vitamin B12, nutrition experts say, since evidence shows that while a vegan diet is generally healthy, B12 deficiency is common among vegans and can lead to a condition known as neuropathy that causes nerve numbness.

“B12 is a problem. It’s one thing we are concerned about,” said Tom Saunders, a professor of nutrition and dietetics at King’s College London. Saunders said he had been “really quite shocked” to find in a study that he and colleagues conducted of people on vegan diets about 20% of them were “seriously deficient” in B12.

Vitamin B12 is found in beef, liver, milk, fish and eggs and can be taken as a supplement in tablet form.

Organizers of Veganuary, a British-based campaign in which people pledge to eat a diet free from animal products for the month of January, say people across the world are currently signing up at a rate of one every 15 seconds. While the concept is Western-led, people from more than 150 countries have signed up.

“Our goal this year is for 350,000 sign-ups worldwide, an increase of 100,000 on last year,” said spokeswoman Toni Vernelli. “We are on course to meet this target.”

Organizers estimate that as many as 10 times more people take part in Veganuary than sign up on the website.

Scientists who presented evidence at a London briefing on the health effects of a vegan diet said that compared to a meat-eaters diet, plant-based eaters benefit from relatively low levels of saturated fat and high levels of dietary fiber.

Evidence shows that vegans tend to be thinner than their meat-eating peers, the scientists said, and tend to have a lower risk of developing diabetes, heart disease and some cancers.

They warned, however, of a rapidly growing range of new plant-based foods available in supermarkets that “look like animal foods but are not really designed to be nutritionally equivalent or better”.

Vegan cheese, for example, can be high in fat, salt and calories, but very low in protein, they said.

“If those foods are high in saturated fat and salt and sugar, you’d expect them to be detrimental to health,” said Tim Key, a professor of epidemiology at Britain’s Oxford University and himself a vegan.

“But if they’re sensibly designed and don’t have high levels of those things, you’d expect them to be good for health.”

(Reporting by Kate Kelland; Editing by Frances Kerry)