Why do Diets Fail?

It's that time of the year when everyone is thinking, 'how many inches extra feet, pounds, stone have I gained over Christmas? How am I going to get rid of it all?' Well we thought we'd take a look at the science of dieting and we've invited Dr Toni Steer to join us. She's from the MRC Human Nutrition Research Lab and, speaking with Chris Smith, she explains the basics of dieting. So what is a diet?

Toni - Normally most people understand diet as something where you restrict your calories in order to actually lose weight. I think therein lies the problem. By saying 'diet' you seem to imply that it's something that you're going to do temporarily. Once you've lost the weight you're then going to go back to what you were normally doing before. I think that that's what most people understand a diet to be.

Chris - So in other words it's flawed from the start because unless you're going for a long-term change you're going to put yourself back in the situation that led to you being overweight in the first place and therefore the weight will come back on.

Toni - Absolutely. I think people set themselves huge expectations of what their weight loss is going to be. I think there was a study in America which asked very overweight women how much body weight they would like to lose. Most of them said they'd like to lose around a third of their body weight, which is a huge amount. We have this big expectation of weight loss and that we're gonna put the years of weight gain right in six weeks with this magic diet.

Chris - I blame the newspapers a little bit because every summer when people are going to go on holiday you see this, 'crash diet, lose x amount of stone in six weeks so that you'll look great on the beach.'

Toni - Absolutely. People focus very much on the aesthetics of weight loss so it's all about getting in to your size ten bikini. What we need to communicate a lot better is actually the health benefits of very modest weight loss. There was a very big study in America looking at people who were overweight and about to develop type 2 diabetes. What they did was over the course of three or four years they got them to lose or maintain a weight loss of around 4 kilos (1/2 a stone). What they found was that, ok they hadn't had a massive amount of weight loss, but they'd significantly reduced their risk of getting type 2 diabetes by up to 50%.

Chris - We can tell people who are a bit chubby, 'your blood pressure's a bit on the high side, if you lose some weight it'll come down and it'll come down enough that we won't even have to give you drugs for high blood pressure.' Even so it doesn't really help in my experience that much.

Toni - It's incredibly difficult. We're living in an environment where there's readily available food 24 hours a day, seven days a week. The environment is incredibly difficult for most people to manage. So yes, the individual can do a certain amount but actually we need to look t some of the bigger issues around: town planning and transport and those kinds of things.

Chris - To get more active? Because presumably that's the bottom line? Energy in = energy out. We either cut down the energy in or we increase the energy out in order to balance things out.

Toni - Ideally you need to do both. So you need to look at both sides of the energy balance equation. You need to eat less and do more.

Chris - If you could just give us a checkpoint plan as to what you would put on a healthy diet or a good strategy to slim down after Christmas. What would you advise?

Toni - Okay. Key strategies for weight loss. First thing is start from where you are. Do a food diary, have a look at what you're really eating, have a look at some of your triggers for where you may be reaching for those extra calories like chocolate bars. Then you need to cut down your energy density. That's looking at calories per bite. So energy dense foods tend to be those that are high in fat. Reducing high fat foods, increasing your low energy density foods which are your fruit and veg, high fibre foods, choosing low fat dairy and getting out of the chair and exercising more.

Kat - Presumably my colleague's strategy of just eating a cucumber for lunch is not doing very well?

Toni - If you try to make really drastic changes to your diet it's really difficult to sustain those over the long term. Your dietary habits, if you think about it, have been built up over years and decades. To break those by just thinking, right that's it, I'm just going to eat cucumber for the next six weeks - it's just not realistic or sustainable.