A quarter of the UK population is obese, and the message of eat less and exercise more is falling on deaf ears. A BBC Horizon documentary examines the idea of personalised dieting. Using ground-breaking research they looked at how genetics and neuroscience help us understand what drives us to eat too much and put on weight, and how hormones affect how we feel. A group of overweightvolunteers underwent a range of tests (genetic, hormone and psychological (attitudes and emotions around food) tests), and were found to fall into one of three groups. After more tests and diet related actvities and advice, the volunteers then followed at home a three-month eating plan specially devised for their group. The aim was for the group to lose 67 stone overall, five per cent of their body weight. The results were impressive; between them they lost 103 stone. Even better, the volunteers agreed almost unanimously that they had found the right diet.
Feasters
Once feasters start eating they find it hard to stop. They never really feel full, so carry on eating. They produce less of a gut hormone GLP-1 that sends signals to the brain to tell us we feel full, so they eat far more before their brains get the message 'Enough'.
They need to eat food that takes longer to digest and keeps them fuller for longer - a high protein, low Glycaemic Index (GI) diet, without any portion restrictions. That means more lean meat like chicken, fish, eggs, nuts and pulses like lentils and beans, but fewer sugary foods, potatoes, bread and pastry. Feasters swapped them for pasta and grains like bulgar wheat that take longer to digest. The GLP-1 hormone is produced low down in the gut and is released in higher amounts by food that is digested more slowly. Eating slowly can also keep GLP-1 levels up. Try eating your meal over half an hour. Eat something you'd normally bite into (a burger, sandwich, banana) on a plate with a knife and fork. Try to have all meals sitting at the table (you'll eat faster if you are standing up).
Emotional Eaters
This group has problems with eating because of psychological issues. They turn to food when anxious, depressed and stressed to try to manage their emotions, in the way other people might have a drink. Stress and anxiety boost levels of hormones like cortisol, which in turn makes us feel panicky. 'Self-medicating' with sugary, fatty, salty foods in particular can stimulate our 'feelgood' response. But that triggers 'catastrophic thinking' - I've blown the diet, so why bother?
They need support to overcome fears and to believe they can resist temptation. They will benefit from joining a weight loss group or using online tools and social media to track progress and keep motivated. They also need to accept occasionally failing with the diet is not the end, and simply start again.
Constant Cravers
They are hungry the whole time and like to snack on things high in sugar and salt. They enjoy food and think about it a lot, grazing throughout the day. Certain genes interfere with the brain's understanding of our fat reserves. If it thinks we have less fat than we actually do, it tells us to keep eating. All the volunteers in this group tested postive for these genes.
Losing weight is hardest for this group. The answer is intermittent fasting - better known as the 5:2 diet, when you eat normally (but healthily) for five days a week, and the reduce calorie intake substantially on the other two days (Horizon volunteers cut down to 800 calories on these days but 500 or 600 calories is usually advised.) This makes the body burn up its fat stores.
Plateau effect
Most of the volunteers (and pretty well everyone following any diet) finds that weight loss tails off around week 8; this is due to metabolic changes. Those who are overweight have a faster metabolic rate than those of ordinary weight just for everyday activities. When weight loss goes below a certain level, the body slows its metabolism to stay at that weight. That is the time you need to do a bit more exercise to 'kick-start' the weight loss process again.
BBC2 Horizon: What's the right Diet for You?: a 3-programme documentary broadcast on 12, 13 and 14 Jan. 2014
