31st December 2018

Dr. Michael Mosley’s Top Ten Diet Myths

There are a large number of diet myths out there, and these misconceptions are a huge obstacle for anyone attempting to eat healthily. So, to help with this, Dr. Michael Mosley has put together his top ten dieting myths – and the scientifically proven facts that show just how wrong they are. 

On my first day at medical school a hundred of us gathered in a lecture theatre to be greeted by the Dean. He talked for an hour but there are only two things he said that I still remember. The first was that, based on previous experience, four of us in that room would marry. He was right; I met my future wife that day. The other thing he said was that while we would learn an enormous amount over the next 5 years, within 10 years of graduating much of what we had learnt would be out of date.  Medicine is constantly changing and unless you keep up you are doomed to cling to outmoded ideas. This is particularly true in the field of human nutrition and dieting. So what are some of the most common and firmly held dieting myths?

Diet Myth 1. It is better to lose weight slowly and steadily, rather than rapidly

There is a widespread belief that if you lose weight fast then you will put it on even faster. But is it true?  In a recent review article titled “Myths, Presumptions and Facts about Obesity” in the prestigious medical journal, The New England Journal of Medicine, researchers put this claim firmly into the “myths” category. After looking at numerous studies which have compared rapid with slow and steady weight loss, they concluded that you would do better to lose it quickly rather than slowly. A recent Australian study backs up these claims. Researchers took 200 obese volunteers and put half of them on a low calorie diet (less than 800 calories a day) for 12 weeks. The other half were asked to cut their calories by 500 a day (enough to lose around a pound a week). They were asked to do this for 36 weeks. There was a very high drop-out rate among the steady dieters: less than half made it to the end of the 36 weeks. Most said they gave up because they were frustrated by the slow rate of progress. By comparison, more than 80% of those in the rapid weight loss programme stuck to it. They were then followed for three years. Although both groups put some weight back on, the amounts were similar. Katrina Purcell, a dietician who led the study, said, “our results show that achieving a weight loss target is more likely, and drop-out is lower, if losing weight is done quickly.” Rapid weight loss isn’t suitable for everyone and if you do decide to lose weight fast you have to make sure you have the right balance of nutrients in your diet.


Diet Myth 2. It is important, before you start dieting, to set realistic weight goals.

This is another of those very popular beliefs which simply isn’t supported by any science. In a study, “Weight loss goals and treatment outcomes among overweight men and women” they asked nearly two thousand overweight men and women about their goals before they started on a weight loss programme. They followed these people for two years and found the that women who had ‘less realistic goals’ were the ones who lost the most weight. In other words, it was better to set a big goal rather than say, “I’ll try to lose a few pounds”. For men there was no link, one way or the other, between how realistic their goals were and how much weight they lost.

Diet Myth 3. Starvation Mode

One of the most popular dieting myths is ‘starvation mode’, the claim that if you stop eating your metabolic rate immediately slows down as your body tries to conserve your fat stores. In a recent experiment researchers took 11, healthy volunteers and asked them to stay in a metabolic chamber (a room where they precisely measure your metabolic rate) living on nothing but water. By day 3 their metabolic rates had risen by 14%. This was probably due to a rise in a hormone called noradrenaline, which is known to burn fat. If they had continued then, I’m sure, the volunteers’ metabolic rates would eventually have fallen, not least because they would have begun to lose significant amounts of weight. But, in the short term, there is no evidence that starvation mode is anything other than a myth.

Diet Myth 4.  You need to eat regularly to keep your blood sugars up

In the study I mentioned above they also measured the volunteers’ blood sugar levels. Although these levels did fall after three days without any food, they still remained well within the normal range. At the same time the levels of fat in their blood shot up, showing that their bodies had switched into major fat burning mode. Eating lots of small meals simply feeds your hunger. Which brings us onto myth number 5.

Diet Myth 5. It is better to eat several small meals a day rather than a couple of large ones.

A common belief is that if you spread out your food into lots of small meals this will increase your metabolic rate, keep you less hungry and help you lose weight. Well, in a recent study, researchers at the Institute for Clinical and Experimental Medicine in Prague decided to test this idea by feeding two groups meals with the same number of calories but taken as either two or six meals a day. Each group ate around 1,700 calories a day. Despite eating the same number of calories the “two meal a day” group lost, on average, 1.4kg more than the snackers and about 1.5inches more from around their waists.  They also felt more satisfied and less hungry than those eating little and often.

Diet Myth 6. Eating breakfast is important if you want to avoid putting on weight.

We are often told that eating a good breakfast is a simple way to control your weight. If you skip breakfast, then you will get hungry later in the day and snack on high calorie junk food. Eating breakfast revs up your metabolism, preparing you for the day. It seems a plausible suggestion but is it true? To test this idea researchers got 300 overweight volunteers and asked those who normally skip breakfast to eat breakfast, while those who routinely ate breakfast were asked to skip it. They weighed the volunteers beforehand and 16 weeks later. So what actually happened? Well, the breakfast skippers who had made themselves eat breakfast lost an average of 0.76kgs. While the breakfast eaters, who had spent 16  weeks skipping breakfast, lost an almost identical amount, an average of 0.71kgs. The researchers concluded that, contrary to what is widely believed, a recommendation to eat breakfast  “had no discernible effect on weight loss in free-living adults who were attempting to lose weight”.

Diet Myth 7. Juicing is a good way to lose weight.

There are juice diets out there promising that you can lose “7lbs in 7 Days” and on a pure juicing diet that can certainly happen. But most of that weight loss is going to be water. The reason is that your body keeps a special store of emergency fuel locked up in your muscles and liver in a form called glycogen. This also binds water. When you stop eating your body burns through the glycogen stores, releasing the water. Not surprisingly, once you start eating normally, your body will replenish its water and glycogen stories and much of the weight will come back on.

Diet Myth 8. Don’t weigh yourself more than once a week

There is a widely held belief that you shouldn’t weigh yourself more than once a week because then you will become overly obsessed with your weight. Well, I weigh myself several times a week, sometimes more and I have science on my side In a recent study they followed 40 people attending a weight loss programme. Some weighed themselves daily, others weekly, monthly or hardly at all. What they found was that the more often people weighed themselves the more weight they lost.

Diet Myth 9. Following a low fat diet is a good way to shed pounds

‘Go on a low-fat diet’ has been the advice of dieticians and doctors for the last half century, despite remarkably little evidence that such regimes are effective. The Women’s Health Initiative, for example, was a massive study that began back in 1991. Approximately 48,800 women were randomly allocated to either a low-fat diet or to a control group (‘stick to what you are doing’). At the end of eight years those on a low-fat diet were just .88 of a pound lighter than the control group and there was no difference in rates of heart disease or cancer. So what should you eat? Choose a Mediterranean diet, rich in fruit and vegetables, but also olive oil, nuts and the occasional glass of red wine. It’s a far better way to lose weight and reduce your risk of heart disease than a low-fat diet.

Diet Myth 10. Doing exercise helps you lose weight

It seems incredibly obvious. Do some exercise, burn some calories, lose weight. But that isn’t what actually happens. Part of the problem is that fat is very energy dense. You would need to run for about 36 miles to burn off a single lb of fat. The other problem is that people often reward themselves for doing exercise by having a treat. If you run for a mile you will burn about 120 calories; but if you then decide to eat a small bar of chocolate, you will consume 240 calories. There are lots of benefits to be had from doing exercise, but losing weight is unlikely to be one of them. That said, exercise is a great way of stopping you putting weight back on once you’ve lost it.

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