Low carbohydrate regimes like the Atkins diet could lead to mood swings and depression and leave slimmers feeling like "an emotional zombie", researchers have claimed.

The controversial high-protein, low-carb Atkins diet has prompted criticism from many doctors who fear it could increase the risk of long-term health problems such as kidney damage, high cholesterol and diabetes.

More research in America has now suggested it could also affect mental health, leaving dieters feeling grumpy, tired, apathetic and restless.

Dr Judith Wurtman and her colleagues, from the Massachusetts Institute of Technology's (MIT) clinical research centre, found that when you stop eating carbohydrates, your brain stops regulating serotonin.

This chemical elevates mood and suppresses appetite, and eating carbohydrates naturally stimulates its production.

Antidepressant drugs make serotonin more active in the brain and help regulate mood.

But carbohydrates raise serotonin levels naturally, acting as a natural tranquilliser.

The MIT research looked at serotonin levels in the brains of 100 volunteers who ate different diets, either with a lot of meat and other high-protein foods, or with more carbohydrates, found in breads and cereals.

They found that the brain only made serotonin after a person ate sweet or starchy carbohydrates.

But they said the "kicker" was that the carbohydrates needed to be eaten in combination with very little or no protein.

This could explain why some people eating a large steak could still feel hungry because their brains may not be making enough serotonin to shut down their appetites.

Because women have less serotonin in their brains than men, a diet low in foods which promote its production could leave them feeling particularly irritable.

Dr Wurtman said: "There are people we call carbohydrate cravers who need to eat a certain amount of carbohydrates to keep their moods steady.

"Carbohydrate cravers experience a change in their mood, usually in the late afternoon or mid-evening, and with this mood change comes a yearning to eat something sweet or starchy."

Dr Wurtman said if someone ate protein when they craved carbohydrates they would become grumpy, irritable or restless.

On top of this, filling up on fatty foods like meat and cheese added to feelings of tiredness, lethargy and apathy.

Dr Wurtman said eating a lot of fat would make you "an emotional zombie".

"When you take away the carbohydrates, it's like taking away water from someone hiking in the desert.

"If fat is the only alternative for a no — or low-carb dieter to consume to satiate the cravings, it's like giving a beer to the parched hiker to relieve the thirst — temporary relief, but ultimately not effective," she said.

Dr Wurtman added: "Serotonin is crucial not only to control your appetite and stop you from overeating, it's essential to keep your moods regulated.