If you have grand plans to change your diet for the healthier in 2018, or indeed before then – there’s no time like the present – it’s important to look in the right places for advice. Generally that means steering clear of celebrities, unless they are celebrity dietitians, which are unfortunately in short supply.

Dietitians are the only nutrition professionals that are regulated by law, and while there are undoubtedly many nutritionists, nutritional therapists and other food experts out there who will give sound advice in good faith, for reliable, science-based guidance, dietitians are the gold standard.

That means when the British Dietetic Association takes issue with a fad diet, it’s worth taking the criticism on board. In an article on its website, the BDA suggests avoiding these five fad diets in 2018.

1. Pioppi Diet

We’ve covered the Pioppi Diet already, speaking to both the author of the book behind the diet – cardiologist Dr Aseem Malhotra – and asking for a dietitian’s opinion of it. It’s not a horrendously bad diet, with advice to eat more vegetables and exercise more always worth heeding, but this take on the Mediterranean Diet still raises the hackles of the BDA because it restricts carbs and encourages 24 hours of fasting each week.

“The book pays homage to eating plenty of fruit and vegetables, fish, olive oil, alcohol in moderation and not being sedentary (much like the current UK government guidelines),” the BDA writes. “But the authors may well be the only people in the history of the planet who have been to Italy and come back with a diet named after an Italian village that excludes pasta, rice and bread but includes coconuts – perhaps because they have a low-carb agenda.

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“The suggestion that this Italian village should be associated with recipes for cauliflower base pizza and rice substitute made from grated cauliflower or anything made using coconut oil is ridiculous. It also uses potentially dangerous expressions like ‘clean meat’ and encourages people to starve themselves for 24 hours at a time every week. Following a more typical Mediterranean diet would also be kinder on the wallet, as the dietary approach in Pioppi is unlikely to be cheap.

“The traditional Mediterranean diet is a healthy choice but this has been hijacked here. Fasting may help weight loss, but the only reason their other advice is likely to help people lose weight is because it involves eating less food and fewer calories.”

2. Raw Vegan Diet

It’s perfectly possible to eat healthily on a vegan diet, as long as you keep an eye on certain vitamins like B12 and D, which are harder to get when animal produce is off the agenda. But there’s no evidence that avoiding cooked food is good for your health.

“While some foods are good to have raw, others are more nutritious cooked – like carrots – and some foods cannot be eaten raw at all – like potatoes,” says the BDA.

“The human body can digest and be nourished by both raw and cooked foods so there’s no reason to believe raw is inherently better. Raw food can be time-consuming to prepare and hard to find when eating out. And it’s not suitable for certain groups like children or pregnant women so family meals could be a challenge.”

3. Alkaline Diet

Boost your health by changing the pH of your blood through avoiding acidic foods and eating alkaline ones! Or not.

“This diet is based on a basic misunderstanding of human physiology,” says the BDA, with admirable patience. “While encouraging people to eat more fresh vegetables is a good thing, the pH of your food will not have an impact on the pH of your blood – and you wouldn’t want it to! Your body is perfectly capable of keeping its blood within a very specific pH range (between 7.35 and 7.45). If it fails to do so you would become very ill very quickly and die if not treated!

“Diet can change the pH value of urine, but testing the pH of your urine just measures the pH of your urine. It is not related to the pH of your blood, which cannot be affected by diet.”

4. Ketogenic Diet

Restrict the carbs in your diet and your body will start to burn fat instead, which increase the amount of ketones in the body. That’s the theory behind this diet.

“Supporters claim it [the ketogenic diet] can help you to lose weight, control hunger and improve your health,” says the BDA. “Worryingly some say it can treat or prevent a number of different types of cancer, which is just not true.

“A carefully dietitian-planned ketogenic diet can be a very effective treatment for people with epilepsy. For weight loss, there’s no magic – the diet works like any other by cutting total calories and removing foods people tend to overeat. Initial side effects may include low energy levels, brain fog, increased hunger, sleep problems, nausea, digestive discomfort, bad breath and poor exercise performance.

“It can be an effective method of weight loss in the short term with careful planning but it is hard to sustain for many in the long term and most of the initial weight loss seen is often associated with water and fluid loss. It is never a good idea to ‘over-restrict’ any one food group (including carbohydrate), because this can mean it is more difficult to achieve a balanced diet overall with respect to vitamins, minerals and fibre in particular. And if you’re eating a high-fat diet, you need to consider the types of fat carefully.”

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5. Katie Price’s Nutritional Supplements

Hopefully you weren’t planning on basing your diet around Katie Price’s advice and meal-replacement products, but just in case you were…

“Rapid weight loss can be motivating, but it is unsustainable,” says the BDA. “Appetite suppressors are not a healthy, advisable or sustainable way of losing weight either. Interestingly the website admits that the diet’s claims have not been evaluated by the appropriate authorities.”

You don’t need to adopt a sachet-based existence to eat more healthily, basically, especially because those sachets are usually very expensive.

“She [Price] may have business talent but she has no nutrition qualifications,” says the BDA. “Meal replacement products work by restricting calories, whoever’s name is on them, and they are not needed as part of a healthy, balanced weight loss plan.”