Why athletes may need more zinc in their diet Although it plays a role in protein metabolism and growth, zinc has never really been associated with enhanced aerobic performance. But all that may be about to change following a recent American study carried out for the US Department of Agriculture. Fourteen young healthy men were... MORE
Zone Diet: cut back on carbs and you risk reducing your performance level
Have carbs had their day?
Imagine a diet that promises ‘(depending on your initial state of health and wellness), increased energy gradual and permanent loss of body fat improved mental acuity…a more restful sleep pattern (and decrease in the amount needed) decreased joint and muscle pain improvement in your cholesterol profile’ surely this must be ‘the’ diet for anyone serious about weight, health and fitness?
As many PP readers will be aware, the ‘Zone Diet’, conceived by Dr Barry Sears and described in his book, ‘Enter the Zone’, promises on the face of it all the above benefits and more, and as a result has become a high-profile fad diet. Early in the 1990s, Dr Sears convinced the coach of the Stanford swimming team in the US to put his team on the Zone diet. Team members went on to win eight gold medals at the Barcelona Olympics in 1992 and a further eight gold medals at the 1996 Atlanta Olympics. Once ‘demonstrated’ in swimming, the Zone diet was adopted by a range of sportspeople including personal trainers, mountaineers, a professional motorcycle racer and two competitive martial artists currently ranked in the top five in every world organisation in karate and kick boxing.
And there’s more. The Zone diet is claimed to help allergies, bowel disorders, chronic fatigue syndrome and many other conditions. Does it all sound too good to be true?
What is the Zone diet?
According to Dr Sears, over the past 100,000 years, man’s digestive system has evolved for the consumption of a diet mainly consisting of lean protein, fruits and vegetables. He argues that 8,000 years ago there were no grains, bread or pasta, and that from a genetic point of view we have yet to adapt to a diet high in grains without suffering adverse biochemical consequences. This might bring a sigh of relief to athletes who are ‘carbohydrated out’ and can’t face any more bread or pasta, so let’s have a look at this diet.
In opposition to the traditional and well-proven high-carbohydrate diet for maximum athletic performance, the Zone diet focuses on protein intake (a daily intake of 1.8-2.2 grams of protein per kilogram of fat-free mass, i.e., total body weight minus fat-weight), and a 40/30/30 ratio of percentage energy from carbohydrate, protein and fat, respectively. The idea is that protein is the key to both maintaining energy levels and optimising recovery. However, the protein intake recommended is higher than that advised by any major health or sports organisation. The International Olympic Committee suggests protein intakes of about 1.2-1.4 grams per kilogram body weight per day for most endurance athletes, with possibly a little more for conditions of extreme energy expenditure such as the Tour de France, and around 1.2-1.7 grams per kilogram body weight per day for strength-speed athletes including body-builders.
Protein, derived either from dietary sources or from muscle breakdown, can be and is used to some extent as an energy source, especially in conditions of carbohydrate shortage (Anderson & Sharp, 1990). A low-carbohydrate diet, such as the Zone diet, in effect increases a person’s protein requirement by increasing the demand for protein as an energy source. Given that protein is an expensive and inefficient energy source, and the concern that high-protein diets may strain the kidneys, it makes sense instead to ensure adequate provision of energy from carbohydrate. In doing so, carbohydrate will ‘spare’ protein, limit muscle breakdown and thus reduce dietary protein needs.
The ‘case’ against carbs
The Zone diet advocates a regular meal pattern (eating at least every five hours) and ALL meals or snacks must individually comply with the 40/30/30 ratio for carbohydrate, protein and fat. This is very limiting, especially for snacks. ‘Favourable’ carbohydrates are certain fruit and vegetable sources; the ‘unfavourable’ ones include bread, cereals, rice and bananas.
The reason the diet eschews most carbohydrate-rich foods is based on the assumption that eicosanoids (types of hormones) have adverse effects on health and physiology, and that insulin is the culprit in producing ‘bad’ eicosanoids, leading our bodies to be ‘out of the zone’ and open to various diseases and general poor health. The main aim of the Zone diet is to prevent surges of insulin kevels which, the author claims, result in fat storage and a reduction in energy levels. The simple truth is that there is no scientific rationale or proof for these claims. Eicosanoids are by-products of normal metabolic processes, and not the devils incarnate that Sears pretends. The pancreatic hormone insulin is necessary for life itself and indirectly supplies energy by transferring glucose from the blood into body cells (including muscle cells) for availability as an energy substrate. In fact, since we do not live on a constant 24-hour drip-infusion of glucose, insulin levels must fluctuate in order to maintain normal blood glucose levels throughout a day’s pattern of food intake and physical activity.
According to Cheuvront (1999), ‘the notion that a 40/30/30 diet can alter the pancreatic hormone response in favour of glugacon is unfounded many of the promised benefits of the Zone are based on selective information regarding hormonal influences in eicosanoid biology. Contradictory information is conveniently left out’.
A low-carb diet means poor performance
The Zone diet as specified is calorie-deficient by any standard and, as with any diet that induces a calorie deficit, will result in weight loss. This is fine if weight loss is the only consideration, but what about the suitability of the diet for training? The Zone diet is low in carbohydrate both as a percentage of total energy and as an absolute amount. There is abundant and reliable scientific evidence to refute the suggestion that a low-carb diet can even support, let alone improve athletic performance. Here’s one recent example from among many.
Helge, Richter and Kiens (1996) subjected 20 untrained young men to an eight-week endurance training programme. Half of the men ingested a high-carbohydrate diet (65% energy from carbohydrate), the other half a high-fat diet (62% energy from fat) for seven weeks. Both groups ate the high-carbohydrate diet for the eighth week. The study clearly showed that consumption of a high-fat, low-carbohydrate diet during an endurance training programme is detrimental to improvement in endurance. Conversely, the importance of maintaining an adequate intake of carbohydrate in order to replenish glycogen stores has been demonstrated time and time again.
Weight loss, maybe, but…?
As with most fad diets, if you have the time and determination to stick with the Zone, you will lose weight. This is because it not only cuts calories but also strictly limits food choices, especially with snacks (which are often the Achilles heel for many slimmers), so that choosing and finding foods to eat is a real problem. It would be virtually impossible not to lose weight if you followed the Zone.
BUT high-carbohydrate diets are also an effective way to lose weight, as long as total calories are limited. In fact, people who consume a diet high in carbohydrate and relatively low in protein (the opposite of the Zone) are said to be better able to lose weight and maintain their weight afterwards.
As for health, it is apparent that vegetarians, whose diets are commonly nothing like the Zone (again, high carbohydrate) have lower incidences of heart disease, diabetes, high blood pressure and certain forms of cancer than those whose diet is high in protein, and more and more evidence is emerging in favour of the health benefits of a cereal- and grain-rich diet. Far from whole-grain foods being ‘unfavourable’, results from a huge 10-year study of 75,000 women suggests strongly that an increased intake of whole grains may protect against coronary heart disease (Liu et al, 1999). Furthermore, from a nutritional point of view, ‘whole grains’, far from being low-value starches, are importance sources of B-vitamins, iron, other minerals, trace elements and fibre.
To sum up, the Zone diet, though convincingly described and powerfully marketed, is far from a breakthrough for the sportsworld. Apart from the lack of supporting evidence, the diet is impractical, expensive, unsociable and limiting. Fitting training sessions around work and family commitments can be hard enough without the extra effort and time needed to plan and prepare personal meals and snacks based on an exact, prescribed formula. Full-time athletes who have struck a rut in their programme and are tempted to try the Zone, and who may have the time, the drive (and the money) to do so, would be better advised to think twice before flying the face of the scientific evidence.
The question to ask about the effectiveness of any fad or gimmicky diet is ‘What was the person eating before?’ Where the diet appears to work, this may simply reflect an improvement on a previously erratic, poorly balanced or deficient diet. At the same time, the psychological aspect should be not overlooked. Placebo tablets, after all, can work very well if you believe in them, and anything that works might just give you the mental boost to put more mental effort into training. The long-term physical effects of an imbalanced diet, however, are something else again.