All you know about dieting is wrong
Eating a low-fat diet won't lead to weight loss, according to the boffins. So, what is making us fatter than ever? John Costello finds out
Eating fat makes you fat seems like a no-brainer. That has been the general belief ever since the 1970s when low-fat diet guidelines were first introduced.
It makes sense. Fat is laden with nine calories per gram, so eating more will make you gain weight. However, that is not what the boffins believe.
Low-fat diets do not work, according to groundbreaking research by Harvard Medical School headed by Dr David Ludwig, that set about to uncover the reason why 70% of Americans are overweight. Don't snigger. We are not much better: 61pc of Irish men and 39% of Irish women are reportedly overweight.
Through his own research and trawling through the work of his peers, Dr Ludwig found that all studies on dietary fat and body fat have shown that fat intake is not a major determining factor of body fat.
The largest clinical trial of diet and body weight, funded by the US-based Women's Health Initiative, found that 50,000 women on low-fat diets had no significant weight loss. Another study, which tracked people on four different diets for a year, found negligible differences between those who followed low-fat and low-carb diets.
"Basically, diets come in and out like fashion," says Mike Gibney, Professor of Food and Health at UCD. "We've had the South Beach Diet, the Atkins Diet, the High Fibre Diet, we've had this sort of diet and that sort of diet, but they come and they go. There are books written on them and glossy Americans selling them, the fact is if they were successful they would be here forever.
"The truth is they are fads. I go along with the view the more personalised the effort that is made with weight the better.
"That's why I personally recommend organisations like Weight Watchers or Jenny Craig or Beauty Slim or what have you, because it is a serious business trying to lose weight and it's a serious business trying to keep it off. People find it hard to do on their own."
Interestingly, two recent studies found the main factor determining changes in body weight and belly fat was actually how your body responds to sugar, carbohydrates or glucose. Therefore, according to Dr Ludwig, testing your insulin level after drinking a sugary beverage containing 75 grams of glucose can best help personalise your diet for effective weight loss.
In one study, 276 people were followed for six years after having their insulin concentrations checked 30 minutes after consuming a sugary drink. This gave an estimate of whether they were high or low insulin producers.
Over the course of the study, records were kept of participants' body weight and waist measurements. Those who were the highest insulin producers had the biggest change in weight and belly fat compared to those whose bodies produced low levels of insulin.
Those people who were high insulin producers and ate low-fat diets did even worse. This is because insulin stimulates hunger and makes you store body fat, according to Dr Ludwig.
So after a high-carbohydrate meal, insulin levels spike while blood sugar drops, making you feel hungry. The result is you crave carbs and sugar.
However, experts here are cautious about embracing Dr Ludwig's findings just yet.
"I think it is far too early for that," says Prof Gibney. "Certainly looking at an individual's genetic make up is wildly premature. But you can individualise information in terms of helping someone chose an appropriate diet to lose weight and help them with suitable physical activity."
He recommends sitting down with a dietician to get personalised information and using a personal trainer to get you in shape. But when it comes to getting information on your blood sugar and insulin levels he is not convinced just yet.
'I do not think that is necessary," he says. "I just think there are enough agencies out there to help people lose weight so I think it is a bit premature to talk about that type of individualisation.
"I would say that the overall impact of genetics on obesity is often overlooked. If you put a thousand skinny people into an obese environment they won't all get fat at the same time or at the same rate.
"Some people are extremely sensitive to extra calories and some people are extremely resistant to extra calories.
"That is a fact of life and the more we can understand about that the better able we will be able to say to people: 'You belong to this category of people who are much more sensitive to weight gain, so we advise you to be much more careful than your friends'. That day could be nearer than we think."
However, his overall advice is to forget your fad diets. The biggest challenge for those who want to slim down is realising it is not easy.
"The relapse rate from diet is unbelievable," says Prof Gibney. "About 95% of people who lose weight in five years will have regained the weight they lost. If dieting was a drug it wouldn't be permitted."
Regardless of advances in science and the role of genetics in dieting, there remains one constant truth -- if your energy intake is greater than your expenditure you will gain weight.
"In order to lose weight you have to eat less calories than you need so that means you have to restrict your food intake and increase your physical activity," says Prof Gibney.
"I remember Dolly Parton was talking to Michael Parkinson about dieting and keeping slim, and she said something I will always remember: 'If you want to lose weight, get your head out of the slop bucket.'"