More people are exercising than 30 years ago, yet obesity rates have more than doubled since 1980 in every country that measures it, even in poor areas of Africa and China. The UK hasn’t escaped the trend: two in three British adults are now overweight or obese, and one in five of our children aged 10-11 are clinically obese.
However, obesity is not only about being greedy. What we eat could be much more important than our total calorie counts, and it is no coincidence that we are also experiencing a dramatic surge in food allergies that used to be rare. But choosing what to eat to be healthy is far from easy.
When I had a health scare five years ago, I decided to investigate what the best diet for me would be. As a practising physician who has written dozens of papers on obesity and studied the causes of many other common diseases for 25 years, I thought it would be straightforward. However, evaluating all the claims out there in print, as well as online, is a minefield, even for professionals, and it’s not made any easier by outdated and flawed government advice. While there is consensus that we should eat more fruit and vegetables and less processed food, there is no agreement on which foods to omit.
What is clear is that, for a long time, we have been ignoring an organ of our bodies that has the power to keep us healthy and to reduce obesity. This is the colon, the part of our lower gut that weighs 4lb and contains 100 trillion microbes, known as the microbiome. We all possess a unique set of microbes like a fingerprint.
Microbe is simply the scientific name for any small creature that you need a lens or microscope to see. Bacteria are the most obvious. They live inside us, as well as on our skin, but we are also home to trillions of harmless viruses and billions of fungi that have evolved with us.
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Cutting-edge science and genetic technology are showing us for the first time how these microbes help to keep us slim, avoid heart attacks and allergies, and even reduce hangovers. This new-found understanding has even shown obesity to be an infectious disease — microbes from overweight humans, when transplanted, can make normal mice obese, and trials are continuing in humans to see if poo transplants from slim people can reverse obesity.
We rapidly gain our gut microbes at birth: we need them to develop a normal brain and immune system, as well as to digest food and make vitamins. Microbes live off the high-fibre food that is hard to digest and reaches the colon. They break down the food and produce small chemicals that, in turn, keep us healthy. When we eat junk food or processed foods that are low in fibre, our microbes fail to produce these healthy chemicals crucial for our immune systems and hormones.
When my son, Tom, agreed to be a Super Size Me guinea pig and consumed only McDonald’s burgers and nuggets, chips and Coke for 10 days, we guessed he would feel unwell, but not that he would lose 40% of his microbe species and diversity. As well as lacking in fibre, junk food may have toxic effects via chemicals such as emulsifiers, preservatives and sweeteners that further disrupt the microbes.
Many people who exist on processed foods can ingest as few as 10-20 food ingredients over a year. In contrast, our ancestors ate about 500 species of plants and animals over a year. They had nearly double the species of microbes we do. We know that the lower the diversity of foods eaten (especially high-fibre foods), the lower the diversity of gut species and the worse someone’s health becomes.
Low microbe diversity is implicated not only in obesity and diabetes, but a whole range of “western diseases”, such as allergies, autoimmune diseases and irritable bowel syndrome.
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What are the best foods for your microbes? The good news is that you can build up your gut health with a few simple rules. The general rule is that you should eat all “real” food.
The soil in our gardens is much like our guts. If healthy, it contains billions of bacteria and fungi that enable plants to flourish and discourages weeds. If you treat your gut like you tend your garden, you won’t go far wrong. We all have a unique soil that needs careful attention, variety and experimentation. Sprinkle on new seeds regularly (probiotics), add natural fertilisers (prebiotics) and avoid toxins such as antibiotics, emulsifiers and pesticides — and above all, keep the garden fed with a rich diversity of high-fibre foods. My new knowledge has changed my boring habits and invigorated my love of food. The key to a healthy gut is diversity.
1 Eat more fibre — doubling your daily intake feeds your microbes. Go for a variety of high-fibre vegetables containing inulin, such as artichokes, leeks, chicory, onions and garlic, plus many other root vegetables and bananas.
2 Eat plenty of polyphenol-rich foods — microbes feed off these antioxidant chemicals to keep our immune system healthy. Most brightly coloured vegetables and fruits, such as peppers and berries, contain high levels. Peanuts and other nuts and seeds have large amounts of polyphenols and can be sprinkled on most meals. Coffee and green tea are examples of polyphenol beverages that have been shown to be surprisingly healthy compared with black tea. Even high-quality dark chocolate (70% or more) can be a healthy treat.
3 Use high-quality olive oil where possible — only the extra-virgin variety has all the polyphenols.
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4 Don’t be frightened to eat more cheese and dairy, but avoid low-fat or processed varieties. A surprising and increasing number of English and French cheeses are unpasteurised and have billions of healthy bacteria and fungi.
5 Eat fermented foods that contain live microbes regularly, such as natural yoghurt, or try newer imports, such as kefir, a fermented milk drink, and kombucha tea. When combined with fibre, they are perfect for your microbes. Try sauerkraut, pickles and kimchi, or fermented soy foods such as miso, natto and tempeh. The longevity of the Japanese and Koreans could be related to their love of fermented foods.
6 Experiment with your food choices — try to have something new every week — and eat seasonally, ideally picking organic foods that are low in pesticides and antibiotics.
The Diet Myth: The Real Science Behind What We Eat by Tim Spector (W&N £8.99) is published on May 12. To buy it for £8.49, inc p&p, call 0845 271 2135 or visit thesundaytimes.co.uk/bookshop