Global rates of obesity and related disease have increased in the 21st Century to epidemic proportions, despite the efforts of the health services, doctors and nutritionists.
We are told that good health is about eating less and exercising more, but is it that simple? Science shows that we all have different metabolic responses to the same foods, so any guidelines will not work for all of us. Many diet recommendations are often based on poor, outdated or biased science.
We are all influenced by deeply ingrained or inherited myths about food (breakfast is the most important meal of the day, fat is bad, fish is good, and so on), and these can be hard to shake. In addition, the global food industry throws billions of dollars every year into manufacturing and marketing processed foods that some believe are designed to leave us wanting more.
There are many reasons for our deep misunderstanding about the science of food, not least that nutrition is an incredibly complex and a relatively new science. It only became a serious area of research in most countries in the 1970s, and it has long been sidelined in medicine.
When I trained as a doctor, 40 years ago, nutrition was just an afterthought, and we learnt more about scurvy than diet and obesity. Sadly, this is still true today in medical schools. Good nutritional research is difficult and expensive to carry out, and it’s not easy to secure funding for the large, long-term studies needed for reliable results.
Until recently, nutritional science also ignored the important role of the gut microbiome: the community of up to 100 trillion bacteria, fungi, parasites and viruses each of us carries in our guts, which outnumber the cells in our bodies. Food interacts with the different species of microbes to produce thousands of chemicals which affect our health. Understanding this process has changed the way we approach food and nutrition.
But there are many reasons to be hopeful. The science is improving at an unprecedented rate. The latest nutrition studies – including those from the Weizmann Institute of Science in Israel, and our PREDICT studies in the UK and USA – use new advances in artificial intelligence and citizen science, and are changing core beliefs.
We can now prove that there is no one-size-fits-all perfect diet. Diversity in our diet is the key to maintaining a healthy microbe population and good health. Conditions such as diabetes can be controlled with low-carbohydrate and high-fat diets, disproving the long-held belief that only medication could keep the disease at bay.
Fat – for years considered the evil of nutrition – is now shown to protect against heart disease and diabetes, not the reverse.
We urgently need to reassess what we think we know about food, and unlearn the myths that have misled us for far too long.
You should count your calories
Calories in equals calories out – this simple rubric has built a diet industry. According to international guidelines from the World Health Organization (WHO), adult males should consume 2,500 calories a day, and females should consume 2,000. But I believe any universal recommended daily calorie intake is at best misleading, and at worst harmful.
The general misconception is that calories are a direct or even remotely precise measurement of how fattening a food is. In fact, although we can accurately measure the calorific value of a meal, the relationship between those calories and our individual bodies is less straightforward. Each of us has a different basal metabolic rate (which can vary by up to 25 per cent in normal, healthy people), and we all burn up energy in different ways.
We also have to remember that all calorie counts are based on estimates. The idea that we can precisely measure the energy value of any food is nonsense, and claiming one dish with 312 calories is better than one with 329 is laughable.
Walnuts, for example, spent years with their calorie content inflated by 20 per cent until it was discovered that much of the fat they contain is not released when we eat them. How the body uses and stores the energy gained from, say, corn on the cob is very different from cornbread or cornflakes. Yet the simplistic calorie-intake theory treats the energy gained from each the same.
Read more about calories:
- Calories and nutrients: the complex calculations we do every day
- How are calories in food calculated?
- Does eating celery really burn calories?
We also now know that the way food is cooked alters its structure: so a steak tartare will provide fewer calories than a burger cooked rare, which will provide fewer than a well-done charred one.
Even more importantly, ultra-processing of food destroys the complex structure of the plant and animal cells, turning the food into a nutritionally empty mush. The average person in the UK actually consumes slightly fewer calories per day than in 1976, but many more of those calories come from ultra-processed food.
The biggest problem with the calorie is not the measurement itself – which does serve some crude purpose – but the way it has given us a false sense of security and precision.
The calorie has enabled the food industry to market unhealthy ‘low-calorie’ foods as healthy, and allowed health regulators to show something quantifiable. But the calorie has been a disaster for the average consumer. We have been fooled into thinking that the effect of food can be easily measured, and conned into eating highly processed foods that fail to satisfy our hunger.
We’re not cars with a standard fuel gauge; we are far more complex and intricate, and rather than basing our decisions about what to eat on a universal, arbitrary and often inaccurate number, we need to learn to understand our own bodies and what they need.
Veganism is the healthiest way to eat
Plant-based diets have become fashionable in recent years. The number of vegans in the UK has quadrupled between 2014 and 2019, with purported benefits for our health, as well as for animal welfare and the environment.
Veganism is good news for other animals and for the environment. But in terms of health benefits, the science is not so clear. Although some studies show that plant-based diets appear to lower the risk of cardiovascular disease, this does not increase the lifespan of vegans compared to non-vegans. A UK study that analysed 5,200 deaths found vegetarians and non-vegetarians had similar death rates.
Although vegans can get all the protein they need from pulses and grains, they do tend to suffer from reduced levels of vitamin B12 and iron. Children who are brought up as vegan are often smaller and have low levels of certain key nutrients.
The food industry has latched on to the popularity of veganism, producing many plant-based alternatives. They are often highly processed and full of salt, sugar and preservatives – one ‘vegan fish finger’ I looked at contained 40 artificial ingredients.
The most positive feature of any vegan diet is the high consumption of plants, which are essential for good health, providing high levels of the fibre that’s beloved by our microbes. But plants can be added to vegetarian or meat-eating diets to obtain the same benefits. So, we cannot say that veganism per se is healthier.
There are many compelling reasons to consider lowering your intake of meat and dairy. Most people don’t require as much protein as we are led to believe, and our planet’s future depends on us all eating less meat. Just don’t be fooled into thinking that vegan is a byword for healthy.
Local is always best
In the US, the average food product travels 1,500 miles (2,414km) before it reaches a consumer’s plate. Britain once produced the most varieties of apples in the world, but we now import 70 per cent, with some travelling over 10,000 miles (16,090km).
There are huge environmental, social and economic costs associated with transporting food around the world, and many people are rightly concerned about reducing food miles. Conscientious consumers try to buy their food locally in an attempt to counteract some of this damage, helping the environment, economy and producers. This sounds simple and can only be a good thing, surely?
The reality is more complicated. A study published in Semantic Scholar in 2009 found that eating lamb from New Zealand is a more environmentally friendly option for most of us in the UK than more locally produced Welsh lamb.
Although the meat travels a long way, it does so in great quantities, and the lambs are reared in eco-efficient farms that use hydroelectricity. A slightly better climate means that grass grows for longer, so the sheep can roam and need less additional feed.
Read more about food and diets:
- The dirty truth about eating green
- Life in the (intermittent) fast lane: the health benefits of time restricted diets
Tomatoes from Spain’s sunny climate are more sustainable than those produced in heated greenhouses in the UK.
Of the estimated 30 billion food miles associated with UK-consumed food, 82 per cent are generated within the country, and over half of these in 2005 were simply due to car trips from homes to local food shops. So buying your food locally may reduce the distance travelled from field to fork, but any environmental benefits are likely offset by multiple trips of less efficient, petrol-guzzling vehicles.
Still, there is no doubt that eating locally can be best when we produce seasonally and choose our collection and delivery transport methods wisely. Locally may be best, but not always, and just make sure you know where it comes from, it is seasonally produced and minimally processed.
You need eight glasses of water a day
We all need water to thrive, but the general recommendation has been to drink more and more, with many guidelines now advising a minimum of eight glasses a day. Is there any evidence behind this recent concern about our going thirsty and drying up? The short answer is no. Studies looking at intakes over 10 years in the elderly failed to show any benefits of extra water on kidney function or mortality.
Clever marketing from bottled water companies has not only convinced us that we need to drink more water, but also that expensive bottled mineral water is somehow better for us.
We now drink more bottled water than ever before, with the global industry growing rapidly at 10 per cent a year. By 2025, the global market is estimated to be worth $215bn (£167bn approx). But research shows that tap water nowadays is perfectly safe, and with added fluoride it is also good for our teeth.
There have been studies showing that tap water contains traces of common pharmaceutical drugs, but they have also found the same levels when testing bottled water. Although water in many areas contains chemicals, such as chlorine (a natural gas that quickly evaporates from water once added), the levels are too small to make a noticeable difference to our health.
Bottled water has devastating environmental costs, and no proven health benefits, but does it taste better? Probably not. Blind tastings have even shown that tap water scores higher than most mineral waters. My advice is stick with tap water: you will be reducing the global environmental cost of half a trillion plastic bottles piling up each year and taking a stand against the power of marketing.
We should all follow the same diet guidelines
For the last 50 years we have been told exactly the amount of calories, fat, protein and carbs we need to eat to be healthy. We are currently told to avoid saturated fats, pick low fat foods, select margarine over butter and eat plenty of starchy vegetables. We are told to eat little and often and never skip breakfast.
There is no good science to support any of these recommendations, and recent science has disproved many of them. So it is no surprise we have tripled the levels of obesity over this time.
As well as the influence of the food industry, the one thing we have overlooked
is that we are all unique. When we gave 1,000 people identical meals in the 2020 PREDICT 1 study and checked their blood, metabolic and inflammation responses, no two people were the same. In our study, even identical twins (who are genetic clones) had different responses.
Some people respond badly to fats, others to carbs, and these short-term blood responses can lead to weight gain and metabolic problems. Recent randomised trials of diet like the 2018 DIETFITS study compared high-fat and low-fat diets and found no difference after a year, but huge differences within the groups.
m,pWe are now in the era of personalised nutrition where most of these outdated diet guidelines can be consigned to history.
We can now measure food responses in real time with glucose monitors, and check fat levels with home blood tests. Meanwhile, testing your gut microbes offers a good prediction of your likely responses to different foods.
It’s important to realise you are unique. Listen more to your body, and less to outdated dogma. Try experimenting with different foods, meal timings and maybe intermittent fasting and see how you feel. If you eat a wide variety of plants and aim to keep your gut microbes happy, you can’t go far wrong.
Exercise will make you thin
I am a big fan of exercise. I enjoy cycling or swimming most days and it undoubtedly makes you healthier and reduces many common diseases.
But it is not the weight-loss cure that it is cracked up to be. Unless you are a professional athlete or regularly running marathons, the chances are that exercise will reset your metabolic thermostat downwards and your hunger levels will increase, you will eat more and subsequently burn less of the calories than you would if you were resting.
The soft drinks companies in particular have been driving this myth for decades, by funding science suggesting that if only we exercised more we could drink as many sugary drinks and snacks as we wanted. The plain truth is that, for most people, you can’t run off a bad diet and good food choices are more important than gym membership.
Pesticides don’t harm you
The modern production of cheaper food in greater quantities has been facilitated by pesticides. Most food products you consume regularly will have been exposed to the chemical glyphosate. Breakfast foods such as porridge oats have been shown to have especially high levels.
This pesticide has been used by farmers since 1974 due to its ability to kill weeds while preserving and drying out the crops and, supposedly, without harming animals or humans. Some studies show, however, that there may be a correlation between exposure to this chemical and a rise in certain blood cancers (lymphomas), with side effects increasing when we look at other pesticides such as organophosphates.
This data is disputed by the multinational companies who produce glyphosate as well as by some health agencies. What is less disputed is the damage pesticides (and herbicides) inflict on the microbial populations living in the soil and in our guts.
One of the roles of our microbes is to stabilise our immune system, so it is perhaps no surprise that some epidemiological evidence (although weak) links pesticides to increased rates of allergic disorders. Although government bodies reassure us that the levels of chemicals used in farming are safe for our health, we are now eating these chemicals for all of our lives.
Particularly vulnerable to subtle effects may be pregnant women and their infants. Further and more robust studies are urgently needed to look at the effects on our microbe populations.
In the meantime, we can try to reduce exposure by washing our vegetables and fruit, growing our own, or favouring organic ingredients, which certainly have a lower exposure levels.
- This article first appeared in issue 356 of BBC Science Focus Magazine – find out how to subscribe here