Epidemiologist and microbiome expert Tim Spector separates truth from fiction when it comes to food, exercise and losing weight. Photo / 123rf
"The best way to lose weight, believe me, is to eat less," said British Prime Minister Boris Johnson as he defended his government's food strategy after proposals for a salt and sugar tax were ignored.
With that "believe me", the Prime Minister hit a nerve for serial dieters: which parts of the vast smorgasbord of advice out there should we be following to ensure our health and happiness?
Along with the recent introduction of calories onto restaurant menus in the UK, it can feel as if we're being shamed into giving up food altogether.
For Professor Tim Spector, the King's College London epidemiologist celebrated for his work with identical twins, as well as diet and the microbiome, all of the above represents a backward step in the public understanding of how humans respond to and process food.
"For the past 100 years, we've been obsessed with calories, and it has really stopped us thinking about anything else," says the 63-year-old author of The Diet Myth and Spoon-fed. He has been working hard to change that thinking.
When The Diet Myth was published in 2015, few people had an inkling of the role that the estimated 100 trillion microbes in our gut play in our digestion. Spector's work has helped to put kefir in our fridges and kimchi in our jars. Via the Zoe Project, the world's largest nutrition study, he has encouraged us all to join up and analyse our unique guts, blood fats and blood sugar responses.
Today, though, his number one myth target is that calories are a useful way to monitor our diet. Not only are calorie estimates often less accurate than we might hope, Spector's studies of twins have shown that humans vary hugely in how much energy they extract from a given food.
The daily allowances for men and women, Spector says, are not based on hard data. So I ask him: what should we be aiming for? Even asking the question, he says, gives credence to the idea that there is a perfect figure. "If it was only 1900, would that make a difference? No, it wouldn't."
And when people are told to avoid calorie-dense foods, Spector says that advice can be taken to be encouraging the consumption of low-calorie drinks and low-fat foods. "It's why we support this multi-billion-pound diet industry of low-calorie shakes and Weight Watchers, and all that other stuff."
So, what other diet myths are we swallowing, according to Professor Spector?
Exercise does require energy, but our metabolism adjusts to that loss by storing more energy as fat the next time we eat.
Our body is programmed to keep our biology steady, known as homeostasis, so if our energy levels are drastically changed with lots more exercise and less food, our metabolism will respond by slowing the weight loss down and eventually put it back on very quickly when we go back to normal activity and food – which is what we see in yo-yo dieters who put all the weight they initially lose back on. "Saying that exercise alone is a good way to reach a healthy weight in the long-term is complete rubbish," Prof Spector says.
This is the diet myth that Spector says trivialises food as fuel. "It goes against everything we should be teaching our children, which is that it's the quality of food, and the difference between foods, that matters." Key to this is that everyone is unique and differs in the way they respond to food.
"Yes, if you lock people in prison and give them no food, they will lose weight. But with free-living people, that just doesn't happen, because your body simply reacts as it's supposed to keep you alive and will change your metabolism."
So as soon as you stop restricted eating, the weight piles back on; this is called the weight set-point theory.
"That's why we yo-yo all the time. It's a real fallacy that just restricting your calories is a long-term solution, because we've been trying that for the past 50 years and we're getting fatter."
Another fallacy is that grazing rather than gorging is a better way to maintain our blood glucose levels, and help us lose weight. Not only does constant eating mean that we never give our gut microbes a well-earned rest, it also gets harder to monitor how much you are eating in a day.
It is a startling fact, Spector says, that "25 per cent of all our energy comes from snacking". We all snack too much.
He would prefer to see people having two to three meals a day and advocates the Mediterranean style of less snacking and taking twice as long as we generally do to eat a meal. "You know, then, what you're eating and you take your time over it and you taste it. It's very different to eating at a bus stop or in the car, or in front of the telly, which has become the British way."
His belief that snacking is bad is also founded on the difficulty of finding a healthy snack that doesn't cause a surge in blood sugars that then leads to inflammation and greater hunger.
"The Zoe team is currently researching snacks, but until that work is finished, I'd suggest eating mixed nuts or peanuts if someone finds it hard to go without something between two or three meals a day. But I think 95 per cent of snacks consumed regularly in the UK are bad for you, items such as crisps, cereal bars and low-fat yoghurts. Be especially careful if a snack claims to be healthy, as they can often be the worst."
"It is the most important meal of the day" is the common rallying cry of the breakfast lover. Not so for Spector, who most days now sits down no earlier than 11am for his breakfast, ensuring 14 hours have passed since he last ate.
Again, it's personal. "A good breakfast is what works for you, but I recommend having a long fasting period beforehand, more than 12 hours, which might mean you need to eat earlier in the evening.
"Breakfast has become synonymous with cereal, and maybe with toast and marmalade. Or more recently, perhaps it's muesli, which is still breakfast cereal with a high sugar content and likely to leave you even more hungry, depending on your body's response to sugar, in three hours' time."
The concept of breakfast itself is new, Spector says, having evolved over the past century or so. That is one reason why he thinks that a majority of people, with a bit of training, could delay their breakfast or skip it completely. "For most people, that's going to be a healthy option."
He has totally changed his own first meal of the day, from a typical British carbohydrate-based plateful to a black coffee. When he eats breakfast, it's because he feels hungry or has done some exercise. It will be a high fat one with fibre and fermented foods, such as yoghurt plus kefir, fruits, mixed nuts and seeds. "And a black coffee. For me and my unique biology, this is a healthy breakfast."
If, when in France, he has a croissant or a baguette, it's a nightmare. "I love them, but I'm often wearing a glucose monitor and it never fails to shock me. I'll just have half a croissant and three hours later I'm really hungry because I've had a big sugar spike and a dip. Annoyingly, my wife, who has much better blood-sugar control than me, can eat them without a problem."
Spector's general suggestion is to experiment with different breakfasts – high fat, high carb, or even leftover dinner – and see how you feel. "Try to get out of a rut of eating highly processed foods to break your morning fast."
If you've booked flights to Spain or Greece this summer then you might already be in training for the 10pm supper. There's probably nothing inherently unhealthy about eating late. You just need to stay up longer afterwards. "In Italy, Greece and Spain, they don't go to bed with a full stomach because they stay up until 1am or 2am," says Spector.
While it's bad to eat just before you go to bed, with the risk of digestion problems, if you do eat late and go to bed late, you might want to adjust your breakfast time. "Countries with a late-night culture don't get up early in the morning. Most people in those countries don't have breakfast as we know it. They have a coffee, often black. So they are still getting a decent 12-hour fasting period."
His research has shown that fasting affects our gut bacteria: several species of bacteria found in people with good health appear in higher levels after a fast. Spector says it's important to work out what time of day suits you best for eating, because everyone is different. "There's growing evidence from Zoe and my own personal studies that once you get over the age of 50, that [timing] probably changes and you get much more variation. I think it's individual. The idea we have been spoon-fed is to fill ourselves up at breakfast and lunch, but this clearly is not right for everybody."
His advice is to experiment and listen to your body. "Try skipping breakfast a couple of times a week when you are busy and see how you feel. Does it make you hungrier? Does it improve or worsen your energy levels? On average, it will do you no harm, and some people feel better and lose weight, but for some people, they will feel that they can't miss it, and that's OK, too."
The following statement may shock you. "Coffee is a healthy drink," says Spector. "It should be in the health drinks section."
Healthier, even, than a fresh orange juice. "Most people wouldn't believe that. There is more fibre in a cup of coffee than a glass of orange juice. Coffee also has more of the defence chemicals, polyphenols, which combined with fibre actually help to feed our gut microbes without any adverse sugar effects. So, we should be drinking more coffee (preferably black) – and if coffee isn't right for you due to caffeine sensitivity, decaf, surprisingly, has a lot of the same benefits."
Tea drinkers take note: "Black tea is not as good as black coffee. Green tea is somewhere in the middle."
For those, like me, who have been congratulating ourselves on not becoming hooked on the strong black stuff, Spector has some wise words: "People might have to force themselves to have their coffee as medicine – and tea as pleasure."
"All our ancestors used to like the fatty bits off the meat rather than the lean bit," says Spector. The bigger discussion point around meat, he believes, is that most people don't distinguish between good-quality red meat and bad-quality meat in processed foods. With the latter, he says, "Studies clearly show that the poor-quality meat going into ultra-processed foods is very bad for you. For your heart, and for cancer."
With the former, he says, "There's no evidence that high-quality meat in reasonable portions is bad for you. But, again, it's about what else you put on the plate." Having a big slab of meat with no space for vegetables isn't a sensible order.
Spector eats one or two high-quality meat dishes a month for nutritional reasons. "I'm not anti-meat, per se, but I'm definitely pro-plant. It doesn't help when we think in black and white; flexitarian is the way forward as we become aware of the environmental impacts."
We're used to hearing the phrase "empty calories" to describe our tipples. However, Spector says that whilst overall alcohol is harmful, he believes giving it up is "slightly exaggerated as a weight-loss tool". People who drink three or four glasses of wine a day would benefit from cutting back to just one, but Spector says: "If you're drinking one to two units a day, I don't think it's going to make much of a dent in a bad diet."
The frequent issue when abstaining from something is, what are you replacing it with? "That's the problem with diet advice," says Spector. "When people give up alcohol, they tend to go for sweet alternatives, which are just as bad."
Making sensible swaps is the challenge. That gin and diet tonic? "Sadly, that's not a healthy option," says Spector. Not only is the gin not gut-friendly, but the diet tonic has artificial sweeteners that are bad for your gut microbiome. "I still drink the odd gin and tonic, but it's good to know the facts."
Another surprising health drink is a glass of red wine, which he says has been shown in studies to reduce heart disease and, in his own studies, to improve gut microbes. "It's also one of my five a day, thanks to the grape skins."
Have you ever eaten a gooey brie and then visualised, with guilt, the clogging up of your arteries? Many of us still believe cheese is bad for us because of the saturated-fat content.
"So many GPs still tell patients over the age of 50 they should avoid cheese, milk and dairy because it's bad for their heart," says Spector. "But there's no evidence that's true."
In fact, there's some evidence that people who regularly consume good-quality cheese (not ultra-processed) have better health because of the way it helps promote a greater diversity of microbes in the gut.
Milk, he says, isn't as beneficial to our health, but "is very useful in some people who lack other nutrients, such as children on poor diets". Providing, that is, you have a genetic predisposition to tolerate lactose, which people whose genetics are northern European generally do.
And if you're wondering whether to pick up a block of butter or a tub of margarine, there's no evidence that butter is worse than so-called "healthy" margarines, which are made artificially with multiple additives. "You'd probably be better off having high-quality olive oil than butter – but I still enjoy butter."
Not all bread is created equal. For Spector, one of the worst diet myths that has gained huge attention in recent years is the idea that gluten makes you ill. For those with coeliac disease or diagnosed gluten intolerance, clearly that can be the case. But for the rest of us, "It's the ultra-processed stuff that causes lots of excess sugar that's the problem," says Spector. That's why so many of us feel tired and sick after eating a lot of it.
Bread is a major source of fibre in the UK diet. "But I think we have a huge problem in this country with being able to distinguish between good and bad bread." Unless you have to, replacing bread with gluten-free alternatives is often worse, in Spector's opinion.
When it comes to diets, bread is often the first suggestion as to what to cut out. Leading to the issue of, what do you replace it with?
"Eighty per cent of people who are working have sandwiches regularly for their lunch, and many will have toast for their breakfast. Tell them to give up bread and they'll take up wraps, which are usually highly processed and give you a sugar spike – that's even worse."
Instead of cutting out bread, Spector says we should be eating less of it, but demanding better quality bread made from wholemeal flour, and ideally sourdough, which is higher in fibre, and not worrying about the gluten. "Gluten's not the enemy, the processing of cheap bread is."
Spector says this well-known advice from the World Health Organisation is arbitrary and not based on any hard facts. "It's widely abused, and very few people in this country follow it," he says.
He advocates an approach featuring 30 different plants (including nuts, seeds and herbs) a week as being more diverse for our gut health.
The major issue with "five a day" is that it doesn't distinguish between different types of fruits and vegetables, some of which contain a lot of sugar, especially fruit juices which are often included and are harmful.
"We've all got our treats, and we shouldn't deprive ourselves of them. But I used to have bananas as my regular daily fruit. Having tested myself using the Zoe programme, I discovered that because of my poorer blood-sugar control, bananas are bad news for me. So I've swapped them for pears or apples, which don't give me the same sugar spike." Realising that all fruits and vegetables are different and have different profiles is important – there's always a healthier choice.
There are a few ways to find out about blood-sugar control; the Zoe programme combines the use of a CGM (continuous glucose monitor), specifically designed muffins, and a simple blood test to understand how an individual responds to sugar and fat. Without testing, it's hard to know your fat response, but you might be able to tell if you have good or bad sugar control simply by listening to your body after eating.
"People who suffer from constant hunger or big dips in energy several hours after eating a carb-heavy meal are likely to have poorer sugar control and should reduce carbs," says Spector.
You've read the myths, so what next? If you're not already doing so, then it's time to think about food differently. "Forget about calories. Eating for your gut microbes is the best way to think about food at the moment," says Spector.
"It's something we can all do. If they are happy, you're basically making your body more efficient at processing the food. You're going to reduce sugar and fat peaks, and reduce stress and inflammation in the body. This should give you more energy, less hunger and help weight loss. Try to aim to eat about 30 plants per week – these include nuts, seeds and herbs."
Let’s ban calories, let’s be citizen scientists and improve our own biology @timspector @Join_ZOE @WiredUK #WIREDHealth pic.twitter.com/YoH4d7kMKY
— Dr Federica Amati PhD ANutr (@FedeAmati) May 26, 2022
Key gut-healthy foods include nuts, seeds, dark chocolate, red wine, olive oil and vegetables such as leeks, onions, garlic and artichokes, which are really packed with chemicals that microbes love. We also need to be regularly consuming more fermented foods, such as kimchi, sauerkraut, live yoghurt and kefir, as a source of natural microbes.
Don't be afraid to experiment. "We're all individuals with different responses to food."
Try changing the timing of your meals. "Perhaps try restricted-time eating. Get tested with a scientifically based personalised nutrition kit, such as Zoe, to work out if you're a carb person or a fat person, as well as the state of your gut health."
Focus on the quality and timing of your meals and ignore the calorie element, says Spector.
"I used to say it's genetic and there's not much you can do, but that's not true. When we did the Zoe Predict studies on twins, genetics had only a very small effect on how you respond to food; your microbes are key."
We need to go back out there and experiment with food, free of assumptions. "It might be that you need a lot less food, but you might need different foods you were told were unhealthy. You might need to eat all your meals late at night and that would change your life," says Spector. "And don't forget your microbes, because they're the ones that will look after us right through into old age."
Eight of the best foods for the gut
Nuts and seeds:packed with fibre and prebiotics that feed our healthy gut bacteria
Artichoke: prebiotic fibre could help curb cravings and aid blood-sugar levels
Red wine: people who drink red wine have more diverse gut flora
Kimchi: a feisty fermented cabbage teeming with beneficial microbes
Dark chocolate: cocoa compounds are fermented into anti-inflammatory chemicals
Live yoghurt: full of protein, calcium and live cultures with gut-friendly bugs
Olive oil: healthy fats in olive oil improve our ability to absorb nutrients
New York Times: Families and experts share their best advice for navigating and coping.