Have you started on a diet for the New Year? As we all know, the real challenge lies in keeping the new regime going after the first flush of enthusiasm. Motivation is obviously the key. Some scientific evidence may help - both in those wavering moments and also to help you tailor your diet to your own particular aims.
Research has shown the healthiest dietary period in the recent history of these islands was during and after the second World War. Children in particular had a healthier intake; they consumed far higher amounts of bread, milk and vegetables. Tea was the most common beverage - soft drinks were scarce. As a result of this survival diet fibre, iron and calcium intakes were much higher than now, and total sugar consumption was half that in the 1990s. This type of diet benefited bone health in later life, as well as providing protection against heart disease and cancer. Do we now have the medical evidence to prove its benefits?
Bowel cancer
High intakes of animal fat, beef and alcohol are independently linked with an increased risk of developing bowel or colorectal cancer. In addition, a diet low in fibre has been implicated in many cancers including colorectal cancers. Although many factors combine before a bowel cancer develops (with family history being especially important), an increase in your intake of fruit and vegetables will have a protective effect.
Osteoporosis
The dietary intake of calcium is extremely important in the prevention of brittle bones. The sooner women in particular address this aspect of their diet, the greater the benefit after the menopause. Older women should drink calcium-enriched super milk as a matter of course. Vitamin D levels are also very important - sunlight is the best source of this vitamin, and older women should try to maximise their light exposure. There is some evidence also to show the benefit of soya protein in preventing and minimising osteoporosis. And while it is not strictly speaking a dietary measure, hormone replacement therapy provides excellent protection against this potentially debilitating condition.
Heart disease
Heart disease is a product of a large number of interacting risk factors. Elevated cholesterol levels are best dealt with by diet, with drug therapy reserved for those who do not respond to diet alone. The "bad" fats are the saturated fats and should be limited to no more that one-third of the total fat intake. Animal fat and highly processed foods are the main things to avoid.
Polyunsaturates are "better" fats, so if you can replace animal fat with this type, then you are making an important change. Oily fish is an especially good source of polyunsaturates, as are vegetables. Folic acid, fresh fruit and vegetables are known to protect against heart disease. You should aim to consume five portions of vegetables and fruit every day.
Phytosterols are the plant version of human cholesterols and prevent the absorption of harmful cholesterol. The food companies have been very quick to latch on to this, and we recently had the launch of the first phytosterol-enriched magarine in this country. Look out for foods containing omega three fatty acids (the "good" fat found in oily fish) when planning your new diet.
Breast cancer
A high fat-intake and being overweight for your height are both proven risk factors for breast cancer. The dietary advice is slightly different for pre and post-menopausal women. Controlling body fat is particularly important for the older woman. This is because overweight women have up to 100 per cent more oestrogen in their bodies than lean women. Breast cancer is an oestrogen-dependent cancer, and women who put on weight after the menopause are significantly adding to the production of the hormone which could then act as a growth promoter for a tumour. The younger woman must guard against an excessive alcohol consumption. Again, the effect of alcohol is to increase oestrogen levels in the blood-stream with a knock-on increase in the risk of breast cancer. Women under 30 run the biggest risk and derive the least benefit from alcohol. Soya acts as a natural oestrogen blocker, and there is evidence to suggest that at least 35 grams of soya a day is best for breast cancer prevention. Eating soya protein is especially beneficial in the younger, pre-menopausal woman.
The antioxidant explanation
You will have gathered from the specific advice given above that fruit and vegetables are always beneficial. The scientific explanation for this has recently emerged. Within each individual cell in the body, the normal biological process can form molecules called free radicals. These are known to be implicated in a number of conditions, notably heart disease and cancer. The body controls the negative effects of free radicals by the protective actions of antioxidant molecules. Antioxidants are found in vitamins A, C and E. The natural way to keep a good supply of antioxidants in the body is to eat plenty of fresh fruit, vegetables, olive oil, garlic and wine - the so-called Mediterranean diet.
Why weight?
Finally, are there any benefits in simply "losing weight"? Research just published in the Journal of the American Medical Association has shown that people who are overweight or obese have a much higher rate of chronic disease. The study looked at 17,000 adults over the age of 25 and found much higher prevalence rates of high blood pressure, diabetes, gall bladder disease and osteoarthritis - rates that increased in line with the severity of obesity.
Gradual weight loss is best - achieved through a combination of sensible diet and exercise. Crash dieting can be dangerous, and in any case the weight loss is usually much harder to maintain following this type of diet. It is best to build in some small treats into any diet, as there is evidence to suggest that an overly rigid approach can cause psychological problems.
So whether you wish to lose weight or work towards a specific dietary goal, the message is clear: diet can help prevent disease if approached in a sensible and focused way.