Some fad diets have no redeeming qualities. The shocking Sleeping Beauty Diet encouraged abuse of sleeping pills and the Cotton Ball Diet involved consuming cotton balls soaked in orange juice.

But not all fad diets are quite that backwards, unfounded and dangerous. In fact, if you do your research and pick apart the principles of some of the world’s most well-known fad diets, you can usually identify the evidence-backed truth that the idea stemmed from.

The Grapefruit Diet is a great example. This diet has been around for about 80 years and it continues to resurface every now and then. The Grapefruit Diet prescribes consuming no more than 800 calories a day and a half grapefruit or glass of grapefruit juice before every meal.

That level of calorie restriction exceeds what most experts recommend, but the addition of grapefruit may actually be a scientifically sound. Researchers at University of California Berkeley recently published findings from a study around the effects of grapefruit on blood sugar levels and fat loss. They found that regular consumption of grapefruit juice could improve levels of glucose, insulin and a fat called triacylglycerol.

Another strange diet with a grain of truth at its core is the Blood Type Diet. The idea is that people should follow a diet specific to their blood type. And the diets vary dramatically – for example, the plan points people with blood type A to a vegetarian diet and type O is told to eat     high-protein.

There’s little to no evidence to back up claims around the health benefits of following the Blood Type Diet. But the truth you can take away is that each person should listen to their body and tailor their diet accordingly.

That being said, there are general guidelines that apply to everyone. Research overwhelmingly shows that a wholefood diet with lean proteins and plenty of plants works very well for the human body. That research has been around for a long time, but when the South Beach Diet burst onto the scene in 2003, it seemed that they had simply packaged nutritional basics into something pretty and turned it into a fad.

It’s true – the foundational ideals of the South Beach Diet are excellent nutritional guidelines. Instead, it’s what was built from this foundation of truth that has ended up being an issue. The modern-day South Beach Diet spruiks branded products containing all kinds of artificial sweeteners, preservatives, flavourings and emulsifiers.

In general, one of the main issues with fad diets is that they’re often too restrictive. They focus on a very small range of foods or, in some cases, just one food. And according to Peter Ungar, a professor at the University of Arkansas, that’s not conducive to long-term wellness.

Ungar says, “Fad diets that restrict the types of food we eat may actually jeopardize our overall health. Such weight loss schemes are based on the erroneous notion that eating only a few specific foods can lead to better health.”

Ungar explains that humans evolved to eat an incredibly varied diet – more varied than any other species, in fact. But despite having access to food from every corner of the world, the modern-day human diet has never been narrower.

“Further restriction of food intake, as prescribed by fad diets, has been shown to promote kidney failure, enlargement of the pancreas and iron deficiency,” says Ungar.

"We are unique in the broad spectrum of foods we take. Primates have a much broader diet than other animals, but we're like super-primates," Ungar explained. "We can eat almost anything we want. That's thanks to our fairly simple gut, our cultural ability to cook and detoxify foods and to our tools, which enable us to break down material that our teeth can't handle."

Restricting our diets to severe degrees isn’t only unnecessary, it can also be dangerous. We’re so lucky to have access to a world of variety when it comes to food – let’s make the most of it!

(photo credit: Elsa's Wholesome Life)