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The fashionable zone diet |
When it comes to diets our patients will often appear to know more than we do. Sometimes we may be asked questions about the latest fad diet or told how good it is, when quite frankly we haven’t the time to read the book, let alone check its credibility. This article cannot solve that dilemma but will pick out just one diet currently in favour for discussion and critical review.
The diet in question is the Zone Diet (ZD) and was developed by Dr Barry Sears, a US biochemist. It claims to have found the answer to weight loss and good health by suggesting that only foods within a certain range of nutrients should be eaten. The ratio chosen is carbohydrate (CHO), protein and fat in a ratio of 40:30:30, which is at variance from the usually recommended 55:15:30 ratio. Interestingly the ZD ratio is similar to that eaten in Western countries where the prevalence of obesity, diabetes and cardiovascular disease are high.
It is a diet that advocates restriction of grains, fruits and vegetables whilst emphasising milk, meat and fat to give a high protein, low CHO diet. Sears attributes CHOs for causing fat gain by releasing insulin which leads to increased storage of fat. However, protein also does this and the combination of consuming excess fat and protein will lead to fat gain.
It is actually more difficult to become overweight from eating CHO compared with fat. CHO and protein contains 4.5 cals/gm, whereas fat contains more like 9 cals/gm. Several steps are required to convert dietary CHO to fat and up to 23% of the ingested calories are burnt in the process. However the conversion of dietary fat to body fat only uses about 3% of the ingested calories.
In low CHO diets the liver compensates by producing glucose by breaking down lean muscle tissue, which will lead to ketosis. Glycogen will be lost from muscle in the first few days on the diet and water will be lost concurrently causing some early weight loss. Other side effects apart from dehydration include light headedness, loss of appetite, constipation, fatigue, postural hypotension, taste changes, halitosis and altered biochemical parameters.
These diets tend to be low in fibre and high in cholesterol and total dietary fat with high consumption of high protein and fatty meat as well as dairy products. This is conducive to high cholesterol, obesity, diabetes, heart disease and certain cancers. In addition, limiting grains, fruits and vegetables greatly reduces other micronutrients such as vitamin B, potassium, fibre, antioxidants and protective plant phytochemicals.
The low fibre content of the ZD is not good for bowel health. Dietary fibre is also good for control of blood sugar levels and therefore diabetes control. The bulk in the high fibre food gives a feeling of fullness and this helps prevent overconsumption of calories. Higher fat diets lead to passive overeating and overconsumption of calories.
So why can people lose weight on the ZD? In addition to the early loss due to fluid loss it has to do with the total number of calories consumed on these diets and on a typical ZD the total calories consumed may be as low as 850 calories, which is well below what is needed for the provision of adequate energy and nutrients. So the weight loss is more due to the low total calorie intake rather than any magic in the ratios of the nutrient groups.
Because of the discomforts and tedium of this restricted diet it is inevitable that having gone on such a diet one will eventually crave to come off and resume a normal diet. What happens then is for some muscle regeneration, water is restored and weight goes on again, mostly as fat. This cycle leads to the so called yo-yo effect seen in many people trying to lose weight but in the progressively upward direction.
It is a dangerous paradox that people who try this ZD will always tell you how good it is for losing weight. Where they struggle is to sustain the weight loss and they spend many years going up and down in weight but with a rising baseline.
Convincing them to change to a higher CHO/fibre, lower fat (particularly saturated fat) diet can be difficult particularly when the ZD habits are entrenched, but there are many health benefits in doing so. Lean meats and low-fat dairy foods should not be forgotten as they provide iron and calcium, which are of particular importance for women. Of course physical activity is always an important component of weight maintenance.
So while this diet may be promoted by Hollywood celebrities and media personalities to a vulnerable overweight population, its long term effectiveness and health benefits should be questioned. As doctors we should be directing our patients away from fad diets towards scientifically valid healthy eating plans.
Further reading: Healthy Eating Healthy Living.
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