New Scientist, 7 June 2016
Fat vs carbs: What’s really worse for your health?
The traditional balanced diet may be way out of whack. To fight obesity and diabetes, doctors and nutritionists are embracing diets that were once called fads. By Clare Wilson
“PEOPLE have told me what I do is dangerous. They have walked away from me at meetings,” says David Unwin, a doctor practising in Southport, UK. Unwin suggests to his patients with type 2 diabetes or who want to lose weight that they do the opposite of what official health advice recommends. He advises them to stop counting calories, eat high-fat foods – including saturated fats – and avoid carbohydrates, namely sugar and starch. Telling people to avoid sugar is uncontroversial; the rest is medical heresy.
But crazy as it sounds, Unwin has found that most of his diabetes patients who follow this advice are getting their blood sugar back under control, and that some are coming off medication they have relied on for years. Those who are overweight are slimming down.
This might seem like just another controversial fad diet, but a growing number of researchers, doctors and nutritionists around the world are backing it, and reporting their findings in peer-reviewed medical journals. Last month, the National Obesity Forum, a UK body for health professionals involved in weight management, made headlines when it overhauled its advice, telling people to ditch calorie-counting, low-fat foods and carbs in favour of fats.
The recommendations provoked a furious backlash from mainstream scientists and dieticians, but they should concern us all. If the advice is to be believed, starchy food isn’t just bad for diabetes, it makes us fat and causes heart attacks. This is analogous to finding that smoking protects people from lung cancer, says David Haslam, an obesity specialist at the Lister Hospital in Stevenage, UK, and head of the National Obesity Forum. “It is terrible,” he says. “We have let people down.”
For decades, standard dietary advice has been to shun fat and fill up on starchy food like bread, potatoes and rice. We are told this is good for our waistlines and our hearts, and is especially important for anyone with diabetes. Guidelines in the UK, the US and Australia, for instance, tell people to fill around a third of their plates with starchy food (see “Food fight”). When the UK government agency Public Health England revamped its “Eat Well Plate” earlier this year, it cut added fats (such as oils and spreads) down to a mere 1 per cent of the recommended food intake.
Fat first came under suspicion when research early last century found that the arterial plaques that can lead to a heart attack contain the fatty compound cholesterol. Then came several studies showing that heart attack rates were higher in countries where people ate more fat, especially saturated fat from meat and dairy foods. Fat was also deemed the enemy of people wanting to stay slim, since it has over twice the calories, gram for gram, as carbohydrates and protein.
From the 1950s onwards, these ideas crystallised into official dietary guidelines, and the health-conscious started switching to leaner cuts of meat, low-fat milk and swapped butter for vegetable-oil based margarines. And they filled up on starchy carbs.
Yet average body weight has continued to climb, as have rates of associated problems such as type 2 diabetes, culminating in what is now arguably a health crisis. In the UK, US and Australia, around two-thirds of the population are either overweight or obese.
The orthodoxy was challenged when some dieters adopted the Atkins diet, which caused a sensation in the early 2000s. This urged people to shun fruit and veg and scoff meat, butter and cream. Doctors warned it couldn’t work and all that saturated fat was a heart attack waiting to happen.
And yet, research showed otherwise. One trial directly compared 156 women on either the Atkins diet or a low-fat diet. After a year, those following Atkins had lost more weight, and their blood pressure and cholesterol profiles were, if anything, better than those on the low-fat diet. Another trial, which lasted two years, had similar results.
The idea that those with type 2 diabetes should ditch carbs has also been led by people defying medical advice. Unwin first learned of it when he called in a diabetes patient who had been missing check-ups. “Her blood tests were amazing,” he says. “They seemed to show that she wasn’t diabetic anymore.”
This broke all the rules. Type 2 diabetes is supposed to be progressive and irreversible. It is the result of our cells becoming increasingly resistant to insulin, a hormone made by the pancreas to help with the uptake of glucose from the blood. The pancreas works ever harder until it cannot produce enough insulin to keep blood sugar levels under control. As a result, blood sugar gets too high after meals and this gradually harms blood vessels, leading to a range of nasty consequences such as foot amputations and heart attacks.
Newly diagnosed diabetics are usually advised to lose weight with exercise, and by eating less fat and more fibre, including bread, cereals and fruit and vegetables. But like most dieters, they usually don’t succeed, and the majority need oral medication to control their blood sugar within a year of diagnosis.
Unwin’s rebellious patient told him she began low-carbing after stumbling across a website that recommended it. As Unwin researched the idea, it started making sense. Diabetics are told to avoid sugar, but starch is basically long chains of sugar and is quickly digested into sugar in the gut.
Yet diabetics are told to eat starchy food just like everyone else to help them eat less fat. Fat is the bigger enemy because it leads to heart disease, says Louis Levy, head of nutrition science at Public Health England.
And even wholegrain carbs, which are recommended, cause our blood sugar to rise, albeit more slowly than their milled equivalents. A slice of wholemeal bread raises blood sugar the same amount as three teaspoons of pure sugar, according to research due to be published by Unwin and his colleagues in the Journal of Insulin Resistance. A jacket potato – archetypal healthy fare – is akin eating 9 teaspoons of sugar (although how fast it is released depends on what you eat with it – fat or protein lowers the speed).
The sugar triggers release of insulin, which stimulates fat storage, and in the long term worsens insulin resistance. Eating fat and protein, in contrast, releases less insulin, and protein is the most filling food group, so will suppress appetite more.
People with type 2 diabetes are sometimes told to eat food with a low glycaemic index (GI), a measure of how quickly blood sugar rises. The faster the blood sugar rises, the harder it is for cells to take up glucose quickly enough to avoid a spike. But a strictly low-GI diet can end up being high-fat by default.
Startled into action, Unwin took the maverick step of offering weekly meetings on this dietary approach to his patients with diabetes or who were overweight. He put them on a less extreme version of the Atkins diet, telling them not only to cut down on starchy food but also to eat lots of non-starchy vegetables and the less sugary fruits, such as blueberries and raspberries. In place of carbs they should fill up on meat, fish, full-fat dairy products, eggs and nuts (see “Food fight”).
It seemed to work. “They weren’t hungry and every week they came back smaller,” he says. Their blood tests showed improvements in glucose control, as well as blood pressure and cholesterol levels.
Unwin published the results from his first 19 patients in 2014. It wasn’t a randomised trial, but there have been such studies in the US. In one study of 34 overweight people with type 2 diabetes, those on a low-carb, high-fat diet with no obligation to calorie count ended up with significantly better blood sugar control after 3 months than those following the low-fat guidelines for diabetes. Three times as many low-carbers were able to stop taking at least one diabetes drug as those on the standard diet.
Unwin’s unorthodox approach has not gone unnoticed. Earlier this year he received a National Health Service innovator of the year award, partly in recognition of the savings being made at his practice, Unwin says. Their per-patient spend on diabetes drugs is about 70 per cent of the local average.
So is it time to overhaul official dietary advice? The National Obesity Forum is certainly leading the charge with its new report. But in an official statement, Alison Tedstone, chief nutritionist at Public Health England, called its contents irresponsible, saying the report was based on opinion rather than evidence and that it ignored “thousands of papers”. Her colleague John Newton said it was at odds with the international consensus. And it has also caused a rift within the National Obesity Forum, with a number of members unhappy about the report.
Critics of the idea argue that mainstream nutritional advice is based on decades of research, involving many hundreds of thousands of people, showing that a diet too high in saturated fats is bad for the heart.
And yet in the past few years, a body of literature has emerged to suggest that the question of fat might not be as straightforward as we once thought. For instance, a recent analysis of past studies found that diets lower in saturated fat are not significantly associated with less heart disease or stroke. Another found that the effects of reducing saturated fat depended on what people ate instead; there was a small benefit from replacing it with polyunsaturated fats, but no benefit from replacing it with carbs. The best kind of study is a randomised trial that alters people’s diet to see how their health changes. Here too, there is conflicting evidence – some trials show a benefit from reducing saturated fat, while others indicate none or even the opposite.
A high-fat diet could also be concealing other aspects of lifestyle or diet, such as too much sugar or a lack of exercise, which may be the real culprits for heart problems.
It also seems fat is a more diverse food group than it first appeared. Oils from plants tend to be unsaturated fats, liquid at room temperature; we thought of these as “good”, unlike saturated fat, mostly found in meat and dairy products and solid at room temperature. But recent studies suggest that dairy fats, which are saturated, do seem to protect people from type 2 diabetes and heart disease. Unsaturated fats too, are a mixed bunch (see “Slippery substance”).
The role of insulin resistance, the key problem in diabetes, also seems to be a bigger player in heart problems than we thought. One recent study found it is a bigger heart attack risk factor for men than high blood pressure, high cholesterol and being overweight. “We have been focusing on the wrong things,” says Aseem Malhotra, a cardiologist at the Lister Hospital, who is a vocal advocate of low-carbing.
“The question of fat might not be as straightforward as we once thought“
Still, many mainstream dieticians remain unconvinced. Julie Lovegrove at the University of Reading, who is a member of the UK government’s Scientific Advisory Committee on Nutrition, says that while not all the studies show consistent findings, “a diet high in saturated fat is not optimal for cardiovascular health”. Susan Jebb, professor of diet and population health at the University of Oxford, takes particular issue with the idea of not bothering to count calories on a low-carb diet, espoused in the new report. “Very few people manage to control their weight without some dietary restraint,” she says.
Such conflicting advice might well leave many of us scratching our heads over what to eat. Almost the only thing both sides agree on is that sugar is bad for you (see “Food fight”). If you tried to hedge your bets and avoid both fat and carbs, there would be little left. A more moderate approach is to limit just saturated fat, added sugars and refined carbs, leaving you more or less with an extra-oily Mediterranean-type diet, high in whole grains, fish, fruit, vegetables, nuts and olive oil.
This diet is higher in fat than the standard recommendations, but a recent large trial of a Mediterranean diet supplemented with extra olive oil or nuts found that either approach cut heart attacks by nearly a third over five years compared with the standard low-fat diet.
People with type 2 diabetes, who are most at risk of heart disease and weight gain, seem to be voting with their feet. Unwin has published his diet advice on a free website and since its launch last November, 110,000 people have signed up, and over 80,000 people have completed the 10-week course. Of 2500 who took a survey 6 months later, the proportion taking diabetes drugs had dropped from 70 to 60 per cent. Although this was not a randomised trial and the results need to be replicated, Unwin thinks it’s a sign of what the diet can achieve without much input from health professionals. “The internet is democratising medicine, and patients have taught me so much,” he says. “It’s a new world – doctors should join in”
The idea of “good” and “bad” fats has come under scrutiny in recent years. The benefits of unsaturated fats, traditionally seen as good for the heart, may vary due to their omega-3 content, which is thought could have anti-inflammatory effects. Then there’s the fact that when most vegetable oils are heated, they form toxic compounds called aldehydes, which have been linked to heart disease, cancer and dementia. So you might be better off frying in butter than sunflower oil.
Many cherished beliefs about cholesterol have also turned out to be wrong. Too much cholesterol in the blood, especially a type called LDL cholesterol, can cause dangerous plaques to build up in blood vessels. But more recently we discovered that smaller LDL particles cause more plaques than large LDLs. And while eating saturated fat raises large LDL levels, small LDLs are boosted most by refined carbohydrates.
That’s alarming because it suggests past research that used total LDL as a proxy for heart attack risk would be misleading – underplaying the dangers of eating processed carbs and exaggerating those of saturated fat.