The good, the bad and the fad: what experts say about the latest diet trends

While diet season is in full swing, the jury is still out on whether trendy diets — like the ketogenic eating plan, intermittent fasting, calorie restriction and the Sirtfood diet, which helped British superstar Adele lose 45kg — are safe and suitable.

Topping the list of eating plans that promise quick results is the keto diet, a high-fat, adequate-protein, low-carb diet that forces the body to burn fat rather than carbohydrates for fuel.

Adele's Sirtfood diet includes sirtuin-rich foods like red wine, chocolate, capers and blueberries that help with weight loss.

Dietitians and doctors have warned that such trendy diets may not be sustainable, hold a risk of long-term nutritional deficiency, potentially lower the metabolism and could bring on weight gain from people not being able to maintain the diet.

But followers of diets like keto, who have shed kilograms quickly, have nothing but praise for them. Durban keto coach Lauren Aaliyah Kolia said she lost 25kg after adopting the eating plan five years ago.

"It literally changed my life. I want to understand what risk there is in eating wholesome food, which people have eaten for generations," she said.

Association for Dietetics in SA spokesperson and dietitian Kelly Scholtz said that as more people struggle to manage their weight, it comes as no surprise that they are searching for a diet that works.

"For that reason I think fad diets will unfortunately always feature somewhere in various forms because they appeal to people emotionally when they are looking for a quick fix - usually fast weight loss."

Scholtz said that for a diet to be considered "really safe", it should "technically be suitable for all individuals to follow at all stages of life, and in all states of health. I would not recommend following any extreme form of restricted eating."

Dr Graham Cassel, a cardiologist at Milpark Hospital in Johannesburg, is "very against the high-fat, low-carb-type diets".

"We've seen some nasty cases where patients' cholesterol has gone up dramatically. These fad diets can cause more problems than they are worth," he said.