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Monday, June 27, 2022

Coffee bad, red wine good? Top food myths busted | Food science

Modern nutritional science is only a hundred years old, so it’s no surprise that we’re constantly bamboozled by new and competing information about what to put into our bodies – or that we sometimes cling to reassuringly straightforward food myths which may no longer be true. In a world where official dietary advice seems to change all the time, and online opinions are loud and often baseless, we ask eight food and drink experts to cut through the noise and tell it like it is.

What’s the truth about coffee?

“I’m surprised that people still think coffee is bad for them,” says Dr Astrid Nehlig, research director of the French medical research institute, Inserm, and one of the world’s leading researchers into coffee, health and brain function. When she first started researching coffee 30 years ago, she often encountered producers who were nervous that their products might be found to be harmful. “But a lot of progress has been made in the last 10-15 years.”

So what do we know, now? “Coffee contains more than 1,000 compounds, so what we are looking at is not just about caffeine,” says Nehlig. “It increases alertness but at the same time relaxes us. It focuses and increases attention, but prevents sleep, especially if you drink too much, or too late.” We are not all equal on this front: caffeine targets our brain’s adenosine receptors but half of us are immune to this effect – which explains all those people who drink espresso after dinner and conk out at 11pm. “It’s also about the accumulation of caffeine during the day, which is related to how we metabolise caffeine – in one group of the population, caffeine builds up in the body, but the other group eliminates it very quickly.”

Nehlig adds: “Coffee has often been accused of being bad for heart health. But we now have global research showing that coffeeit is protective against cardiovascular disease, stroke and coronary heart disease, and decreases mortality linked to cardiovascular issues.” Nehlig says there is also clear evidence that coffee protects against type 2 diabetes, regardless of body fat; it’s definitely protective against Parkinson’s disease and almost certainly against cognitive decline in general. Coffee does not increase our risk of cancer. “It’s neutral, or even protective in some cancers, like the liver, colon, endometrium and some non-hormonally dependent breast cancers.” Quite why this is, isn’t yet known; Nehlig’s hunch is that it’s to do with coffee’s range of antioxidants.

This isn’t a licence to knock back as many flat whitesas possible, though. “Research shows adults shouldn’t go over 400mg a day, which is 4-5 small cups, and no more than 200mg in one sitting.” (Coffees from high-street chains can contain as much as 300mg in a large serving.)

“For some people caffeine will either trigger anxiety or worsen symptoms of anxiety,” says Murray Carpenter, author of Caffeinated: How Our Daily Habit Hooks, Helps and Hurts Us. “Some who really suffer from anxiety have never experimented with eliminating or minimising caffeine.” (My own anxiety got so bad that I had to give up caffeine during the worst of the pandemic in 2020. I still miss it.) Caffeine also worsens insomnia. “In both scenarios, I think it’s important that people experiment with changing their caffeine habits and see what improves,” says Carpenter. It won’t be a silver bullet for everyone. “But if you don’t experiment, you won’t know.”

Are alternative “milks” better for us than dairy?

“Are plant milks highly processed foods? Yes: they are,” says Dr Duane Mellor, registered dietitian, British Dietetics Association spokesperson and senior teaching fellow at Aston Medical School. “There is a massive green and health halo attached to plant-based foods, which is not necessarily informed by the composition of the foods themselves. Do we know if the same outcomes are as likely for people eating other highly processed foods, like loads of bacon sandwiches? Not yet.”

Spraying graffiti on a milk carton
Illustration: Lalalimola/The Guardian/Alamy

As Mellor points out, the research hasn’t yet been done but it will also be hard to analyse, because people consuming plant-based dairy replacements may tend towards a diet lower in other highly processed products (although ultra-processed meat and cheese replacements are a growth area), and may share other demographic qualities that place them in generally healthier groups. “It’s OK if you want to use them to whiten your coffee, but I wouldn’t rely on them as a major source of nutrition,” he says. Mellor would prefer people choose, for example, naturally vegan desserts, rather than readymade desserts made with plant-based dairy replacements.

“We are a bit over-reliant on dairy as a source of protein,” says Mellor, but the solution may not be plant-based replacements, which, apart from soy, don’t contain much protein, anyway – almond milk can be as little as only 2% nut, giving it just 1g of protein per 100ml, similar to oat, whereas dairy milk contains about 3.5g of protein per 100ml. Most milk alternatives contain added nutrients to mimic those in cow’s milk (although usually not the iodine that we mainly get from dairy), but organic plant milks are rarely fortified.

What about the emulsifiers and stabilisers in milk replacements, which some scientists think could destabilise the bacteria in the gut? “The evidence isn’t strong yet,” says Mellor. Lots of foods naturally emulsify, like egg yolk and mustard, so they’re not intrinsically bad. “But there are some synthetic ones which – possibly because they are synthetic – may interfere with the gut microbiome, which then has a theoretical impact on health. People get a bit worried about stabilisers such as carrageenan [from seaweed] and xanthan gum [from fermented sugar]. When you extract these compounds and put them into a food product, do they behave differently than when they are in the natural food? We don’t know. It’s all theoretical.”

Surely it’s good to avoid the saturated fat in dairy? “The main source of saturated fats in the British diet is baked goods – pies, biscuits and cakes – and these processed foods, which are high in fat, refined carbohydrate and salt, may be more of a problem than dairy. Some saturated fats uniquely in dairy may actually reduce risk of heart disease: fermented dairy such as unsweetened yoghurt and some cheeses probably reduce risk, milk is neutral and butter perhaps slightly increases it.”

If plant-based dairy substitutes aren’t great, nutritionally, what about other kinds of milk? Goats and sheep lactate for a shorter time than cows, meaning more offspring are needed to generate milk – raising even more ethical and sustainability issues than cow’s milk already does. For some people, goat and sheep milks seem to be easier on the gut. “It’s a controversial area, but sheep and goat milk have less-to-no A1 beta casein which have been claimed to make them easier to digest. (This is different to lactose – all contain lactose.) But evidence from studies is not supportive.”

“It’s vital people ensure they are getting adequate sources of important micronutrients,” says Professor Barbara Ryan, gastroenterologist, clinical professor of gastroenterology at Trinity College Dublin and one of the Gut Experts. She recommends taking vitamin D to protect bone health, regardless of dairy consumption. “We have diagnosed young women in their 30s and 40s with osteoporosis as a result of cutting out dairy in their 20s and not ensuring that they were getting adequate calcium from other sources. A couple of pregnancies, followed by breastfeeding, increased their requirement for calcium, and this simply was not met by their diet.”

Is red wine the acceptable face of alcohol?

“There is no good evidence that red wine is good for you,” says Professor Sir Ian Gilmore, liver specialist and chair of the Alcohol Health Alliance UK. The original claim that it might be is partly based on resveratrol, a polyphenol in wine which may be associated with good health outcomes, particularly cardiovascular – but in quantities far higher than those found in a couple of glasses of rioja. “A therapeutic amount of resveratrol would only be found in pints of red wine,” says Gilmore.

Man climbing out of a red wine glass
Illustration: Lalalimola/The Guardian/Getty Images

“Often this comes from mouse studies,” says Dr Sadie Boniface, head of research at the Institute for Alcohol Studies. “They give mice a really high dose of polyphenols which could be the equivalent of 100 bottles of wine in one go. Polyphenols are not unique to red wine: they are found in blueberries and other dark fruits, so it doesn’t make sense to say you need to drink red wine to get the health benefits. We know that alcohol causes about 200 medical conditions: you can’t drink to get the benefits without also increasing your risk of other types of diseases.” The World Heart Federation published a research summary and policy brief in January which showed that alcohol is definitely not good for cardiovascular health.

Another reason for this myth’s persistence relates to how non-drinkers and moderate drinkers are compared in some research (sometimes quietly funded by the alcohol industry). “There’s this idea that moderate drinking is good for you and that you live longer than if you don’t drink at all,” says Boniface. “But the best research looks in detail at other aspects of people’s lives and has found that it’s not the moderate amount of red wine that is good for you, it’s other health behaviours. So you might have a good diet and life circumstances – you’re not living in poverty, breathing in lots of pollution – and those behaviours and lifestyles cluster in people who are moderate drinkers: they’re people who are living healthier lives. That’s why they live longer. Not because there’s a sweet spot in terms of how much alcohol you should drink.”

And how do they compare with abstainers? “About one in five adults don’t drink, and there’s lots of research to show that they are on average in worse health than people who are moderate drinkers. Maybe they have another health condition or they are on a medication that would interact with alcohol, but those people have typically worse health outcomes on average. So moderate drinkers then artificially look healthier.”

Neither Gilmore nor Boniface want to come across as killjoys. “I’m not advocating for everyone to be teetotal,” says Gilmore. “I’m sure public health experts do drink alcohol,” says Boniface. “There’s the more social-cultural side of alcohol, the fact that people enjoy drinking and it’s a huge part of our society and the way we socialise. Those other sides shouldn’t be ignored. But nobody should ever be drinking because they think it’s good for them,” she adds.

For Gilmore, the public health message on alcohol isn’t entirely about individuals, but about reducing the general burden on the NHS. “People think that the most harm comes from people drinking two bottles of gin a day, but actually the bulk happens among people drinking 20-40 units of alcohol a week – because there are so many of them.”

Can red meat really be that bad for us?

“Red meat has become the villain of the piece,” says Rob Percival, author of The Meat Paradox: Eating, Empathy and the Future of Meat, head of policy research at the Soil Association and an expert in the politics of meat. “And chicken and white meat have been given a free pass, alongside plants. But there’s nuance in the science, which isn’t often communicated in the press and is lost in the debate on social media,” he says.

Some observational studies have indeed suggested that red meat is associated with various lifestyle-related diseases (a meta analysis published in 2021, for example, found a correlation between red meat eating and a wide range of cancers), “but those studies have found that association more in populations consuming a highly processed, western-style diet”. Plus many of the studies lump red meat in with processed meat, despite them being very different foods.

“Unpicking the role of meat relative to other factors is actually quite complicated,” says Percival. “There’s a body of evidence which shows that if you’re eating a healthy omnivorous diet with lots of plants, then that association is nullified: red meat isn’t contributing to premature mortality. The overall picture seems to be that red meat can play a helpful role in addressing deficiencies in micronutrients [such as zinc, vitamin B12 and potassium]. It’s not the villain it’s made out to be, specifically in relation to cancer. The World Health Organization found that there was a good body of evidence associating processed meats with a higher risk of cancer, and a slightly looser body of evidence associating it with red meat, but they acknowledged that red meat can play a healthy role in the diet and that there were ambiguities in the science.”

What’s less ambiguous is the question of quantity. The NHS says that a diet is high in red (and processed meat) if you eat more than 90g a day, and that cutting down to 70g (averaged out across the week) is lower risk, along with having weekly meat-free days. Seventy grams may equate to less than you’d think: 490g (70g x 7 days) means in one week you could eat just one steak (225g), two pork sausages (140g) and a quarter of a pack of mince (125g); not a lot for the average meat eater.

A mountaineer climbing a wall of pasta
Photograph: Lalalimola/The Guardian/Getty Images

Should we cut the carbs?

“Carbohydrates are made up of simple sugars or chains of sugars, and are a major source of energy,” says Elaine McGowan, clinical dietitian, co-author of What Every Woman Needs to Know About Her Gut, and the other half of the Gut Experts.

“Simple sugars contain glucose which is rapidly absorbed from the gut into the bloodstream. This rush of glucose causes a spike in insulin, which in turn causes a glut of glucose to be taken up into the body’s cells. The cells don’t generally need this rush of glucose for immediate use and so the glucose is stored, and some is converted to fat.” This is why carbs are associated with rising levels of obesity, as well as diseases including type 2 diabetes.

But that doesn’t mean all carbs are bad (almost no food is entirely good, nor entirely bad; it just depends on how much of it we eat). Instead, we could limit simple carbs – “‘white’ foods including white cereals, breads, crackers, flour, sugar, biscuits, cakes, confectionery, juices and sweetened drinks”, says McGowan – and eat complex carbs instead, which are found in vegetables, fruits, whole grains, nuts and seeds.

“Complex carbohydrates are made up of long, branched chains of sugars which take quite a bit of time to digest in the small intestine. The sugars are absorbed much more slowly into the bloodstream. As a result, insulin levels do not spike quickly and the sugar is taken up by the body’s cells in a controlled way, more closely matching their energy needs, so less sugar is converted into fat or stored in other ways. Complex carbohydrates are high in fibre, low in fat, very filling, feed your gut microbiota and contain important vitamins and minerals.”

As with all things, moderation is key. “One potential downside we see, is that some people are now eating too much fibre (the daily recommended amount is 20g-35g a day) and this can trigger gut symptoms.”

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