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Diet act: advising on the latest food fads

Fashionable diets promising fast and effective weight loss are always being promoted, but what about the risks and benefits to patients?

Weight loss diets are big business. New diets seem to pop up every year, many boosted by celebrity endorsement. Some are crackpot fads soon discredited or dismissed as ineffective, unscientific or even dangerous. Others become firm favourites. Currently popular are the 'intermittent fasting' 5:2-type diets (examples include the Fast Diet and the Two-Day Diet) involving two 'fasting' days a week, and the Paleo diet based on the sorts of food our hunter-gatherer ancestors might have eaten. There are also low-carbohydrate, high-protein diets such as Atkins and Dukan, and a spate of low-GI (glycaemic index), high-fibre diets including South Beach.

Many patients seen in primary care will be on one or other of these diets - perhaps because they have type-2 diabetes, hypertension, back pain or arthritis, they've been picked up through NHS Health Check, or maybe they're attending with symptoms linked to the side-effects of excessive fasting. How safe are these diets? How effective? And what can the primary care nurse do to advise and support patients in the throes of dieting?
All 'successful' weight loss diets tend to have three things in common: they reduce calorie intake enough to bring about a gratifying initial loss of weight; they are reasonably easy to adhere to; and they can be adapted to maintain weight loss over the longer term. Some involve calorie counting; some restrict or eliminate particular foods or nutrients; some involve weekly group meetings and weigh-ins; some offer ongoing advice from specially trained counsellors; some provide texted prompts or phone apps; and some are so drastic that they need medical supervision.

Side-effects are an issue. Too few calories and the dieter risks hunger pains, halitosis, headaches, nausea, constipation, faintness, tiredness and weakness. Some of these problems are linked to electrolyte imbalance caused by the initial loss of water that accompanies the breakdown of glycogen in the liver and muscles. Others are linked to ketosis, when ketones are released into the bloodstream by the breaking down of fatty tissue (which is why crash dieters' breath often smells of nail varnish remover).

Very low calorie diets (VLCDs)

These type of diets include those offered by Cambridge Weight Plan or LighterLife. They rely on strict calorie reduction using specially formulated meal replacements, particularly during the first phase of the plan. The calorie intake for Cambridge can be as low as 415 calories a day (compared with the typical adult female's daily requirement of 2,000 calories and adult male's 2,500 calories) but this is gradually stepped up as the plan progresses. An important element of these plans is support provided by specially trained advisors.

Weight loss on VLCDs can be quite impressive, but side-effects are quite common in the early phases. Tiredness and dizziness are common problems, as is constipation. The British Dietetic Association advises that VLCDs below 1,000kcal a day should not be continued for more than 12 consecutive weeks, and anyone going on a diet of less than 600 calories a day should consult their doctor first.

Low-carb/high-protein diets

These include popular diets such as Atkins or Dukan. These are also multi-phased but based on 'normal' food rather than meal replacements. With the Atkins diet, carbs are severely restricted for the first two weeks while allowing unlimited fat with plenty of meat, eggs, cheese, butter, fish and shellfish and some salad vegetables. Thereafter more carbs are introduced and weight loss becomes more gradual. The Dukan diet is another multiphase plan, similar to Atkins but with fat restriction as well as carb restriction in the first phase. Both of these diets have rigid rules ruling out whole groups of nutrients, particularly in the first phase, which can cause dietary imbalance and problems such as constipation through lack of fibre.

Low GI diets

Examples of low glycaemic index (GI) diets include the South Beach diet. These favour unprocessed plant-based wholefoods, with more fibre and carbs with a low glycaemic index, meaning that they take longer to digest and absorb and are therefore slower to release glucose into the bloodstream. This can be helpful for patients with insulin resistance and poor glucose tolerance. Whether this means low GI diets are less likely to lay down fat in adipose tissue is debatable and not well supported by the evidence. They are however more 'filling' which helps to suppress appetite.  

Intermittent diets

Intermittent diets include the 5:2 diet, the Fast Diet, and the Two-Day diet. These involve a very-low-calorie element, but not in a phased plan. Instead they comprise two non-consecutive 'fasting' days a week, with the other five days of normal healthy eating. 'Fasting' days are 600 calories for men and 500 for women. There is currently little evidence on either effectiveness or safety, but they are relatively easy to adhere to. Interestingly, NHS Choices advises consulting a doctor before undertaking any such diet.

Mediterranean-type diets

These include the Paleo diet. A 'Mediterranean' diet is a generic term for the widely accepted healthy eating diet - plenty of fruit and vegetables, wholefood grains and pulses, nuts, fish, eggs, lean meat, olive or sunflower oil and some dairy. In other words, low on saturated fat and sugary foods. This is good for cardiovascular health and prevention of some cancers, but not necessarily brilliant at controlling weight, unless care is taken to keep to keep to food groups in the proportions recommended by the Department of Health.1
The Paleo diet follows what is assumed to be something close to our hunter-gatherer ancestors' diet - seeds, nuts, fruit, veg, leaves, eggs, meat and fish (when they got lucky), and herbs and spices. The usual version has no refined sugar or salt, and only limited amounts of cereals, potatoes and dairy. So it is basically a low carb, low fat, moderate protein diet, with a narrower choice than the usual Mediterranean diet.

In primary care practice, much of the support needed by patients on these various diets will be in managing their expectations, keeping them motivated and advising on side-effects. They should understand that any rapid early weight loss (largely water) is likely to 'plateau' or 'yo-yo' within two or three weeks and that they should aim for no more than a steady 0.5-1.0kg per week after that. They should also be encouraged to become more active.
Some commissioners allow referral to a local commercial slimming group such as WeightWatchers or Slimming World and there may be access to a community dietitian. But more often than not it's the primary care nurse who has to hold the front line in the battle against obesity.