If only you and I were dogs or rabbits – how much easier this column might be to write! For in advising a scientific approach to dieting, I could advise “Eat plenty of red meat, and gnaw bones at times”, or “Keep munching the grass, along with an occasional carrot”.
Yet we’re omnivores, and whilst this means we can thrive on a variety of diets, it also makes it very tough or even impossible to recommend an ideal human diet. Clearly, though, there is something very wrong with typical modern diets, since an obesity epidemic is sweeping the world. According to the World Health Organization, worldwide obesity has nearly doubled since 1980, and by 2008 more than 10 percent of the world’s adult population were obese – with a body mass index (BMI: weight in kilograms divided by the square of height in metres) of at least 30.
Overweight and obesity are now the fifth leading risk for global deaths, from diseases such as stroke, heart disease and some cancers. The health risks plus the desire to look better lead many people to aim to lose weight, albeit you shouldn’t overdo this, given recent research found that being excessively thin means more chance of dying than being overweight.
The death this week of 25-year old British socialite Peaches Geldof may serve as an example of how extreme dieting can prove fatal. She had described shedding weight through “juicing” – surviving for a month at a time on nothing but vegetable juice. In response, Cath Collins, a spokeswoman for the British Dietetic Association (BDA), told The Sun newspaper: “Peaches joins a long line of celebs who are brain dead when it comes to nutrition,” and perhaps prophetically warned, “'Peaches is at high risk of electrolyte abnormalities which could lead to acute cardiac arrest.”
The BDA is highly critical of fad diets, even publishing an annual list of the Top 5 Worst Celebrity Diets to Avoid. The latest number one was the clearly crazy Breatharian Diet, in which people can supposedly live on fresh air alone. Others included a gluten-free diet, never mind whether you actually have trouble with gluten, along with the protein-heavy Dukan Diet, for which even founder Pierre Dukan warns there are issues including lack of energy, constipation, need for extra vitamins and minerals, and bad breath.
“The simple fact is, there is no ‘wonder diet’ just as there are no ‘super foods’,” noted Sian Porter, consultant dietitian for the BDA.
There is, however, an evidently villainous category of food ingredients: artificial trans fatty acids, or trans fats. These are created by converting cheap liquid vegetable oils into shortening and margarines, which are semi-solid at room temperature, have long shelf-lives, and withstand repeated heating. While these qualities endeared them to the food industry, their consumption has been associated with health problems ranging from cardiovascular disease, through infertility, to Alzheimer’s disease. As a result, their use may be banned in the US, where health officials estimate their elimination could prevent 20,000 heart attacks a year. In Hong Kong, there is mandatory labelling if they are present in food.
The trans fats had often taken over the culinary roles of natural saturated fats, which are found in meat and dairy products. These have long been considered unhealthier than the unsaturated fatty acids of fish, nuts and vegetable oils, yet in March researchers published an assessment of 72 studies, and concluded there was little difference in the risk of heart disease or other cardiac events. Despite the conclusions being swiftly criticised, the notion of artificial fats bad, natural fats not so bad, remains.
“Aha!” you might exclaim. “We should all eat like cave men and women, and lead long, vigorous lives just as our distant ancestors did, with rippling bodies tuned like racing cars.”
Not only does this seem a wonderfully romantic notion, it has also led to Paleo dieting, with books published and online information abounding. But what does science say?
A few small-scale studies indicate that there are indeed benefits from eating unprocessed foods including meat, fish, fruit and vegetables, but without dairy products or grains. The most recent of these appeared this month, and found that over a two-year period, the women who followed a Paleo diet lost significantly more weight in six months than those on a traditional low-fat diet, though there was little difference in weight loss by the end of the study.
Unsurprisingly, the Paleo Diet is championed by several celebrities, and pilloried by some scientists. A scathing article in Scientific American noted that we have changed genetically since Palaeolithic times, such as by developing lactose tolerance in response to eating dairy products. Then, evidence shows our ancestors did suffer cardiovascular problems, and few lived beyond 40. Added to which is the difficulty in determining diet compositions, especially given modern peoples depending on wild foods range from South American hunter-gatherers who constantly complain of hunger, to Inuit relying on seals and other sea mammals.
Nor have we stopped evolving, or become identical when it comes to responses to food. Research published in Nature Genetics last month found that people vary in the number of copies of a gene for producing an enzyme to help dissolve starch. This may have resulted from a shift towards eating more starch, and people with more copies of the gene appear significantly less prone to obesity.
Also last month, an assessment of the Health Survey for England found that people eating seven or more portions of fruit and vegetables a day were 42 percent less likely to die than those eating one portion, with fresh vegetables conferring the strongest health effect. Some writers promptly scoffed at the impracticality of eating so many portions, yet for a role model you might consider Australian cricketer Peter Siddle, a vegan who devours up to 20 bananas each day.
If the thought of eating more like a ravenous oversize rabbit than a disciplined dog seems daunting, science does have comforting news as Easter approaches. Experiments with mice fed on high fat diets showed that an antioxidant in non-processed dark chocolate helped keep their weight down whilst improving glucose tolerance, which could counter diabetes. Another new study discovered that some stomach bacteria ferment dark chocolate, creating compounds that lessen inflammation of cardiovascular tissue, thus reducing the risk of stroke.
Perhaps, then, you can include a little chocolate in your quest for a healthy diet. But remember that celebrities are entertainers, so look to science for the skinny on what’s really good or bad for us.