Bursting the fat bubble
Low-fat diets are good for your health, right? Not necessarily, says Lucy Atkins
Tuesday July 16, 2002
The Guardian
Last Sunday, millions of Americans choked on their bagels as they opened the New York Times magazine. "What if it's all been a big fat lie?" yelled the headline. The author went on to suggest that we have all been duped: the supposedly healthy, low-fat, high-carbohydrate diet that for 25 years our governments have been telling us to eat is making us fat. Our obsession with cutting out fat, says one eminent Harvard doctor, is probably at the root of the current obesity "epidemic" in the US. (In Britain, too, more than half of us are now overweight or obese.)
We all know the theory: fat makes you fat. It clogs your arteries. It has nine calories per gram, compared with four for carbohydrates and protein. It is greasy. It is often extremely tasty. It is bad for you. So cut it out, we are constantly told, and fill up on carbohydrates such as bread, cereal, pasta, rice (as well as fruit and vegetables).
Which is largely what we do. If you are at all health conscious, you probably had cereal with low-fat milk this morning; maybe toast with a low-fat spread and jam; possibly even a banana. In other words: a low-fat carb-fest. Which is exactly what a growing number of US doctors believe is ruining our health.
Dr Walter Willett, chair of the department of nutrition at Harvard school of public health, does not mince his words: "The low-fat campaign has been a failure." Ongoing data, gathered from nearly 300,000 people in large-scale studies, shows, he argues, that "a low-fat diet is not an effective strategy for weight control." Indeed, "it may lead to weight gain."
One fact is undisputed: we are about 10% heavier than we were 20 years ago. Most scientists believe this is because we live in a "toxic-food environment", assailed on all sides by unhealthy snacks, fast foods and the temptation to do no exercise. Willett agrees that such a lifestyle is bad for us, but also argues that when we cut fat from our diets, we rely more on carbohydrates and low-fat products which are packed with sugar. This makes us gain weight. The reason is partly sociological, he explains - most of us have come to believe that you only get fat on fat calories, so we simply eat too much other food.
But he believes there is also a physiological reason: "Carbohydrates can cause our metabolisms to hold on to fat. They also influence appetite and can cause us to overeat." This is what Dr Robert C Atkins, author of the Atkins Diet Revolution, has been claiming for 30 years. Reviled by health professionals on both sides of the Atlantic, Atkins' theory that carbohydrates - not fat - make you fat has spawned a whole dietary subset of "low-carb" regimes (like The Zone or Sugar Busters, responsible for the dramatic shrinkage of celebrities such as Jennifer Aniston and Geri Halliwell).
On an Atkins-type regime, if you fancy it, you can eat deep-fried butter balls for breakfast but you can't drink fruit juice, or eat an apple. Outraged health professionals have long pointed out that such no-carb diets are harmful - to our arteries, our livers, our vitamin intake. But now doctors such as Willett are finding themselves in the rather uncomfortable position of agreeing with Atkins, at least on some points.
Willett's argument revolves around insulin. Your body produces it when you eat carbohydrates. It regulates your blood-sugar levels, but also helps your body store fat. In the few hours after eating, you burn carbohydrates for energy and store the excess calories as fat. When your insulin has been depleted, you start to burn that fat as fuel.
Willett's claim is that "if you eat too many carbohydrates, you produce too much insulin, so your body does not get the signal to burn fat. Some people may therefore store fat more readily when they eat carbohydrates than they would if they had got those extra calories from other sources."
Many other nutrition specialists disagree. Dr Susan Jebb, of the MRC human nutrition research group in Cambridge says this is simply "not proven". In experimental conditions, she says, if you give two people the same amount of calories - one lot from fat, the other from carbohydrates - "there is no significant difference in how their bodies store the fat". Indeed, "there is every reason to believe that fat calories are 'more fattening' because, in the real world, it is easy to overeat on them."
Different types of carbohydrates, says Jebb, affect the body in different ways. Refined carbohydrates - sugar, or anything made with white flour - are known as "high-glycemic index carbohydrates". Your blood sugar rises quickly when you eat them and gives you a surge of insulin. A few hours later your blood sugar levels crash. You get suddenly hungry, and crave more carbohydrates.
What, then, should we be eating? Interestingly, this is where the two sides of the debate edge together. Both agree that we should not cut out carbohydrates - rather, it is the type of carbohydrate that matters. Willett says our diets should be dominated by whole grain foods along with plant oils (such as olive, soy, corn, sunflower, peanut). Jebb agrees. "You should avoid refined foods and sugars," she says, "and try to eat mainly unrefined carbohydrates - like whole grains and vegetables". This will stop your blood sugar levels - and therefore insulin - from the surge-crash cycle.
Both sides also believe that we should still cut back on saturated fat (such as fried foods, butter, cheese). We should, however, eat more monounsaturated and polyunsaturated fats (nuts, fish, avocados, seeds and vegetable oils). Willett believes that this will not provoke us into eating more calories, because a diet that includes fat is more satisfying, and gives us less temptation to snack because we are not fighting the glucose/insulin swings. What is more, some fats are essential if we want to stay healthy. "We are starting to see serious health problems in people who have completely cut fat from their diets," says Willett, citing fat-free salad dressings as a major culprit (they deprive people of "healthy" oils).
It does, then, look like the familiar "cut the fat" message is subtly out of date. The current (1991) UK government dietary guidelines advise us to get more than 50% of our calories from carbohydrates. There is no obvious distinction between refined and unrefined carbohydrates. And all "fats" - cooking oils, butter, margarine - are lumped together in the "eat sparingly" category.
Jebb recommends that our daily diet should contain 30 to 35% healthy fats; 15 to 20% protein (mainly fish, poultry and eggs), and the remainder from carbohydrates - unrefined where possible (this would be slightly fewer than current government guidelines suggest). "If you want to lose weight," she says, "you should eat the same balance of food groups. But in smaller portions."
In short, the bottom line hasn't changed: you still get fat if you eat too many calories. And the message now remains fairly straightforward: replace saturated fats with "healthy" ones. Eat whole grains and vegetables instead of refined foods such as cake, white bread and biscuits. If you do this, the chances are that in the absence of sugar highs and lows, both your bathroom scales and your arteries will reward you for it.
http://www.guardian.co.uk/health/st...,755926,00.html