Celebrity nutritionist Gillian McKeith is a prominent promoter of diets with no basis in scienceMcKeith Research LTD

With the amount of information thrown about on what not to eat, it is hardly surprising that most people have a special diet of some sort. Vegetarian, vegan, gluten-free, keto, paleo – the list goes on and on. Some claim health benefits, some claim weight loss, and some even claim to cure cancer.

These claims generally appear to be well founded in science, but most mas well have just materialised out of thin air. As long as a publicly-respected – and thin – person endorses the diet, a mass of people will follow. Write a witty book about the faults of the current fad diet (whatever that may be), and those who have failed and failed again will gladly choose it as the new Bible. Information about these diets reads uncomfortably like political propaganda, with the prize being the perfect, unattainable body. Our bodies have become a battlefield; eating well has become a war. 

One of the newest fads is the gluten-free diet, popularised by the cardiologist William Davis in his New York Times bestseller Wheat Belly.  Commonly used by coeliac sufferers as the only viable treatment plan, this diet has been taken oven by people looking for a quick detox or weight loss solution. Davis called the current generation of wheat – ‘Frankenwheat’ – toxic and addictive, a drug designed to make us eat more junk food. Gluten, a protein found in wheat, has been demonised as the cause of skin rashes, type 1 diabetes, gut inflammation, and dementia, in addition to being  responsible for weight gain.

As a cardiologist, his words carried a lot of weight, but how scientifically sound are his claims? While Davis states that modern wheat is nothing like the wheat of the 1950s, independent studies suggest that the nutritional value of wheat has not changed over the past 150 years. Wheat still contains the same macronutrients and a variety of essential micronutrients, such as potassium, iron and vitamin B. All of these claims are nothing but fear-mongering, trying to create a scapegoat for weight gain, while ignoring the nutritional value of wheat. In an attempt to crucify gluten, Davis has cut a valuable source of nutrients out of many people’s lives.

Many other fad diets have done the same, including the keto diet, which advises eating little to no carbohydrates. The pseudoscientific principle behind this low-carbohydrate diet is the state of ketosis. This occurs naturally during a period of starvation when the body has used up all sugar stores. To survive, the body then starts to burn fat. By not eating any sugar, the body will naturally finish using sugar stores and then turn to fat for energy. In such a sense, on a keto diet the body will, as its advocates suggest, become a ‘fat-burning machine’. But if more fat is eaten than metabolised, guess what: it will still stay in your body as none other than fat. So, yes, while keto does theoretically turn your body into a ‘fat-burning machine’, eating extraordinary amounts of butter, cheese, and meat is not going to help anyone’s waistline.

In the search for the diet holy grail, even evolution has become a sacrifice. In the paleo diet – short for Palaeolithic – practitioners believe that humans have not evolved fast enough to digest the food we currently eat. The aim of this fad diet is to eat like a caveman would. Ironically, during the Palaeolithic Era, humans adapted to eat whatever they could find due to the varying climate, while fruits and vegetable looked very different from how they do today. The assumption that modern humans can reproduce the hunter-gatherer diet is absurd. Not only is it physically impossible to find the vegetables and fruits that were eaten thousands of years ago, many humans back then also suffered from malnutrition and often died from starvation. The glorified paleo diet is anything but Palaeolithic, and certainly not scientific. 

For weight loss, the only effective strategy is eating less than you expend. The currency of energy expenditure in the body is usually measured in calories (or kcals). To demystify the seemingly complicated ‘calories’, their nomenclature must be explained. In the UK, energy in food is usually measure in kcals, which is one kilocalorie, or one thousand calories. One calorie is the amount of energy required to raise the temperature of water by 1°C at one atmospheric pressure. Translated into food, fibres contain 2kcal/gram of energy, sugar contains 4kcal/gram, ethanol contains 7kcal/gram, and fat contains 9kcal/gram.

As long as energy intake stays below energy expenditure, the body will use whatever energy stores  it has – be it sugar, fat, or protein – to maintain basic metabolic functions; in other words, to stay alive. Basic metabolic processes aim to maintain body temperature, basic brain function, basic respiratory function, all of which require energy. When the rubber hits the road, the only reliable way to lose weight is to control calorie intake and expenditure.

To simplify weight loss down to calories in vs. calories out may be convenient, but in truth weight is governed by a much more complex system of nerves and hormones. Recent studies have found that the secretion of the ghrelin hormone, which alters the perception of hunger, is usually disrupted in those who suffer from obesity and metabolic diseases. Such studies suggest that obesity may be caused by illness, and not simply gluttony.

Leptin is the hormone responsible for feeling full. It tells the body when to stop eating, in order to regulate energy intake. Where mutations in the hormone's structure have been found, these lead to some form of obesity. Clearly, then, weight is a more complicated matter than just having self-control.

To add fuel to the fire, a mother’s diet during pregnancy can dramatically change the child’s future weight. A study in 2003 found that, by giving pregnant mice certain dietary supplements, their offspring became thinner. Recent studies of a similar kind have been published which suggest that weight is a staggering 75 to 85 per cent genetically determined. These studies have sent only one message: there is so much we have yet to learn about our own bodies.

The complexity of the human digestive system should not thwart those who want to better their health. Instead, it should serve as a liberating reminder that failures sometimes happen, and that small setbacks are not always catastrophic. On the most basic level, only counting calories in vs. calories out is a fail-safe method. This equation for energy gives some semblance of order to the chaos that is our appetites. Though we should always aim to better ourselves, be kind on those who lost the genetic lottery, fighting all instincts in order to stay healthy. As the obesity epidemic rises, let’s not forget that we’re all fighting against a disease, not against each other, and not against our bodies

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