The researchers conducted a survey of social media users who followed health food accounts, assessing their social media use, eating behaviours and orthorexia symptoms. The results were published in 2017 in the journal Eating and Weight Disorders.

“You shouldn’t blindly follow diet trends or eat a certain way just because someone else is,” says Cyrus Luk, a dietitian at Matilda International Hospital and an executive committee member of the Hong Kong Dietitian Association.

“A diet or meal plan that works for one person may not yield the same results for you, due to differences in age, gender, lifestyle, and so on.

“If you have any questions related to nutrition, a registered dietitian is the best person to speak to. Dietitians are clinically trained and will advise you based on your current diet, health status, activity level and lifestyle. Their recommendations are also backed by scientific evidence. Sound nutritional advice should come from large-scale human-based studies.”

Here’s what Luk has to say about the most popular diet trends on social media today:

Water-only fasts

While human studies on water fasting are minimal, Luk says that people can lose up to 0.9kg (2 pounds) a day over a 24- to 72-hour water fast. Drinking only water for a short period may have some benefits, he adds.

“Small-scale and short-term studies from animals and cells indicate that water-only fasting may reduce some disease risk factors, such as by improving insulin sensitivity and blood pressure.

“It may also stimulate autophagy, a process that helps our body break down and recycle damaged molecules from cells. However, many of these benefits may be short-lived and have not been tested on humans on a large scale.”

Water fasting carries risks. In the short term, you may experience a drop in blood sugar levels and low blood pressure – conditions that may cause dizziness and lightheadedness, increasing your risk of fainting and accidents.

“Water provides no energy or nutrients, so, in the long run, you’ll lose a substantial amount of weight,” Luk says. “Unfortunately, much of this weight is water, glycogen, body fat, and even muscle mass. Malnutrition may result, affecting your immunity and general health.”

As for claims that water-only fasting is a great way to “detoxify” your system, Luk stresses that there’s no evidence that our bodies need to be detoxified by eliminating solid food.

Juice-only diets

“Fruits and vegetables are still the healthiest when consumed whole. Juice-only diets often result in a severe calorie deficit and fast weight loss. Like water-only fasting, most weight loss comes from the loss of water, glycogen, body fat and muscle.”

In the short term, he says, juice-only diets are associated with diarrhoea, because of the high fructose intake; fatigue because of the energy deficit; as well as nausea and dizziness.

In the long term, consuming large amounts of fruit juice is associated with metabolic syndrome and obesity because of the juice’s high fructose content. Malnutrition may also result, because of the lack of protein and fat.

“Clean” eating

“Clean” eating is based on the idea that the best way to eat is to avoid refined, processed foods, and consume only organic, whole ones.

Luk adds that some processed foods can still be included as part of a healthy diet.

“For instance, canned fish in brine is a good source of protein, healthy fat, and calcium if the bones are consumed; frozen fruit and vegetables are high in fibre, vitamins, minerals and antioxidants; and canned beans make a convenient meal and are a good source of protein and fibre.”

When buying processed food, Luk recommends reading the label to make sure the food isn’t high in sugar, fat, salt and unnecessary food additives.

Omitting entire food groups

Avoiding carbohydrates by adopting regimes such as the keto diet has been touted as being effective for weight loss. However, Luk says that only short-term results have been studied and these results have been mixed. Only a few studies have been conducted on the diet’s long-term safety and effectiveness.

“In the short term, risks of the keto diet include keto flu, which includes symptoms like tiredness, nausea and headaches, due to the lack of carbohydrates as an energy source for the body. You may also experience mood swings, since our brain needs sugar from carbohydrates to function.”

Additionally, the keto diet is focused on protein and fat, but Luk says that high consumption of these may increase our risk for kidney and liver diseases.

Unrefined whole grains such as oats, rye, millet, barley and spelt are an especially nutritious source of carbohydrates. These are high in fibre and nutrients compared to refined carbohydrates like white bread and white rice.

“What I eat in a day” videos

Many of these videos push hyper-restrictive diets, which may promote eating disorders and disordered eating patterns. They also invite comparison with the viewers’ own eating habits and this may lead to low self-esteem.

“These meal plans are often associated with nutrient deficiencies, and you might lose weight initially, but in the long run you’ll find them difficult to sustain,” Luk says.

“Detox” diets or “cleanses”

According to Luk, there’s no real definition of a “detox” diet, but such diets almost always involve fasting, eating specific foods, avoiding “harmful” ingredients and/or taking supplements.