The Zone Diet Review

Diets come in all shapes and sizes – high protein diets, low fat diets, low carbohydrate diets, low calorie diets – and some involve very specific (and complex) rules and food choices.

Not all diets suit everybody, and whilst many diets appear to work in the short-term, it may not be for the reasons the diet claims. It may be possible for you to achieve the same benefits by following a different dietary regime that is easier, healthier and more enjoyable.

Before making any diet decisions, it is always best to equip yourself with the right information on a particular diet and to get a good understanding of the nutrition principles behind it. I would also recommend you speak to your doctor or a dietitian before embarking on any new diet regime.

In this blog post I review The Zone diet and attempt to summarise the claims and nutrition principles behind it.


The Zone is a dietary program that aims to achieve a state of optimal health through the balancing of certain hormones – namely insulin, glucagon, and eicosanoids.


To achieve the ‘zone’, the author, Dr Barry Sears, has tailored meal plans to activity level, gender and percentage of body fat, but are all based on the ratio of:

  • 40% carbohydrates;
  • 30% proteins; and
  • 30% fats.

By following this ratio, it is suggested that insulin control is improved, resulting in weight loss and overall wellbeing. However, it is important not only to eat meals in this ratio, but also to avoid certain foods in each of the three macro-nutrient groups (the groups being carbohydrates, proteins and fats) – with a particular focus on avoiding carbohydrates such as rice, pasta and bread.


A high-carbohydrate, low-fat meal, Sears claims, will trigger an increase in blood sugar levels, which results in an excess release of insulin. This increase of insulin signals cells to convert glucose (from carbohydrates) into glycogen, which is then stored in the liver and muscles, and facilitates the storage of fat in fat cells. Conversely, when blood glucose levels are down (by having a low carbohydrate based meal) the pancreas will release glucagon signals in the liver that will trigger the release of glycogen, which is then converted back into glucose and used as energy. If blood glucose levels are low, fat will also be burned for energy.

Sears therefore claims that increased insulin levels tell the body to store carbohydrates as fats, which leads to weight gain. By controlling the ratio of proteins to carbohydrates in your meals, Sears believes you can keep insulin levels in balance and will have better control of your weight, and be more efficient at burning fat.

Sears discusses at length the role of eicosanoids (signalling molecules in the body), labelling them as super-hormones, which when unbalanced, lead to the majority of human disease. Sears claims that his recommended ratio of 40:30:30 will ensure a balance of these hormones.

Sears doesn’t hold back in attacking current healthy eating guidelines and nutrition research. He claims that current ‘expert’ recommendations, which are high in carbohydrates, are making people fat.

Sears is highly critical of high-carbohydrate diets, and goes so far as to claim that there has not been enough time in evolution for humans to adapt to agrarian diets (diets that include foods from agriculture e.g wheat and rice).


The role of insulin is not as simple as The Zone makes out. Sears has made the science of insulin seem very simple, but it is actually very complex.

Insulin is not only produced by carbohydrate based foods (such as cereals, bread, pasta, fruit etc) but also protein and fat based foods (e.g meat, fish, lentils). Studies have actually shown that fish, beef, and lentils produce more insulin than white pasta.

Insulin is vital for the normal functioning of the body. Its role is to regulate the amount of fat (from fatty acids), glucose (from carbohydrates) and amino acids (from proteins) in the bloodstream. However, Sears focuses on the fact that insulin stores fat, resulting in weight gain, which leads to obesity – It isn’t that simple.

The Zone doesn’t take into account the role of another important hormone – leptin. Leptin is a hormone produced by fat cells. Its main role is to regulate the body’s energy intake and energy expenditure. This includes regulating appetite and metabolism. Studies have shown that when people do not produce sufficient levels of leptin they have incredible appetites and overeat – leading to obesity.

Leptin is required in large amounts in the body in order for the brain to communicate with fat cells. If leptin can not make this communication, fat metabolism is adversely effected. Carbohydrate restricted diets lower leptin, which as mentioned above, is linked to over eating.

There is no evidence to support Sears’ claims that eating a Zone favourable diet will provide you with optimal health and increased athletic performance. A few anecdotes do not constitute as sound scientific theory.

The so called ‘studies’ Sears has quoted in his books on The Zone can not be classified as proper scientific research as they did not involve control groups. Because of this, you don’t know what effect or how much effect, The Zone diet contributed to the changes in people and how much it was a result of other factors (such as exercise intensity, changes in calorie consumption etc).

The Zone is very heavy handed on carbohydrates. Sears suggests the removal of the bottom section of the food pyramid (or the bread, cereals etc section of the food plate) would result in a zone favourable diet. Sears’ criticisms stem from the view that humans genetically favour a diet of our hunter-gatherer ancestors, and so have not adapted to the diet that came with the dawn of agriculture (10,000 years ago). This is a very controversial topic amongst both nutritionists and anthropologists, and one which is beyond the scope of this blog post.

Current nutritional guidelines are not making people fat. Sears makes the bold claim that it is government dietary guidelines, which are high in carbohydrates, that are making the population fatter.

However, just because dietary guidelines exist doesn’t mean they are followed. I find it difficult to believe that the eating habits of the average person are influenced by a set of government guidelines and therefore hesitant to conclude that rising global obesity levels can be linked to such guidelines. Ask yourself the question – are your specific food choices, like what you had for breakfast, really driven by a set of government guidelines?

Also, when nutritionists talk of a high carbohydrate diet, they are referring to the ratio of carbohydrates consumed. They are not suggesting that you eat as much carbohydrates as you like.


After all of my criticisms, you may think that I don’t have anything nice to say about The Zone. However if you are looking to lose weight, this diet can work, but not for the reason it claims. Although it is not mentioned in any official The Zone material, this diet is actually a low calorie diet. Regardless of the 40:30:30 percentage, if your meals are the size suggested you no doubt will be eating less than you normally would and you will lose weight.


As mentioned in my criticisms above, The Zone is based on a hypothesis rather than strong scientific theory, so there is no evidence to support the 40:30:30 ratio.

Creating meals and snacks that have the correct ratio of nutrients is difficult to achieve. To combat this, Sears has organised foods into ‘blocks’ (carbohydrate blocks, protein blocks, and fat blocks) and has created a formula of how many blocks should be eaten at each meal and snack. In reality though, no food is a pure ‘block’ of just carbohydrates, proteins or fats. So it would be very hard (if not impossible) to follow the 40:30:30 ratio of eating prescribed by The Zone.


The Zone has become a very popular diet in the last few years, and has many avid followers. However any weight loss benefits from this diet are disguised behind ‘scientific’ explanations, and a complex dietary recommendation of 40% carbohydrates, 30% proteins, and 30% fats.

Hopefully the future will tell us whether The Zone can stand the test of scientific scrutiny, so until (if at all) that day comes, I will not be an advocate for this diet.


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