WHY DO WE EAT TOO MUCH?

The amount we eat will ramp up this festive season, but why are we so inclined to consume more even when we’re not celebrating?

Since medieval times the festive season has been an excuse to get down to some serious overeating. The average Briton will consume 6,000-7,000 calories on Christmas Day alone. And it’s not hard to see where the excess comes from: turkey and all the trimmings, booze, Christmas pudding, mince pies, nuts and don’t forget the cake, complete with marzipan and icing. It doesn’t stop there – there’s the office party, New Year’s Eve and festive drinks with friends. That’s nine days of uninterrupted consumption.

An average of 15,000 calories of food, 18,000 calories of alcohol and another 3,000 calories of snacks per person is consumed over the festive period, which is two or three times the recommended daily intake. That’s according to a survey of 1,000 adults carried out last year by weight loss company Vitagetics. But why do we overeat – at Christmas and other times too? Some answers can be found in a mountain of research in neuroscience, physiology and psychology and the latest evidence is bringing us closer to understanding the problem.

Theories on overeating abound. We may eat too much because food activates pleasure centres in the brain. Or maybe we fear waste and feel we must always clean our plates – a drive inherited from our hunter-gatherer ancestors whose lives veered between feast and famine. Some people may overindulge in an attempt to fill a psychological void created by childhood abuse, or to relieve stress.

HOW MUCH IS TOO MUCH?

With all this research, it’s perhaps surprising to learn that there’s actually no official definition of overeating. Government recommendations state that a man needs 2,500 calories a day to maintain his weight, a woman 2,000 calories. But they do not say that eating more than this is classed as overeating. “The term ‘overeating’ is loaded because it assumes that there is such a thing as normal eating. In fact our food intake fluctuates widely from day to day,” says Jeffrey Brunstrom, Professor of Experimental Psychology at the University of Bristol whose research focuses upon the role cognition plays in eating. “Maybe the best way to describe overeating is when you feel you have eaten more than you felt you should, or wanted to, and are experiencing the soporific effect healthy weight increases the risk of diabetes, heart disease and several forms of cancer. Obesity also impairs selfconfidence, body image and relationships. There is also the psychological trauma associated with eating disorders such as binge eating (consuming 2,000 to 3,000 calories at a single meal) and bulimia.

At its simplest, the body can be likened to a car. It needs to fill up with fuel regularly to keep going. Sensations of hunger and satiety act like a fuel gauge, regulating our feeding behaviour and involve various hormonal signals passing from stomach to brain. Appetite is stimulated when the stomach is empty and releases a hormone called ghrelin into the bloodstream, while fatty tissues decrease production of the hormones leptin and insulin. These signals are transmitted to the lateral hypothalamus, a region of the brain involved in feeding and other motivated behaviours, generating the sensation of hunger.

Eating ceases under the influence of several satiety signals. When the tummy is full, a signal is sent via the vagus nerve, which has many endings in the wall of the stomach. The signal goes up to neurones in the medulla at the base of the brain, signalling that it is time to stop feeding. If you eat slowly, and with attention, this satiety signal is likely to come through louder and stronger than if you wolf down your food, or chat while you are eating, when it is more easily overridden.

But humans are more complicated than cars – they are actively motivated to carry out survival behaviours, such as eating and sex, because they give pleasure. The smell, taste, texture and sight of food can all give pleasure. Research has shown that dopamine is released in the reward centres of the brain when palatable foods are consumed. Clearly, some foods are more palatable than others.

Palatability in foods tends to boil down to the same three factors, however – fat, the four-hour period after a meal had been consumed. Volunteers consumed milkshakes with the same calories, sweetness and taste – except that one contained fast-acting or ‘high glycaemic index’ (high GI) carbohydrates, while the other had slower-acting or ‘lower glycaemic index’ (low GI) carbohydrates. As is well known, consuming high GI foods leads to a rapid rise in blood glucose, followed by a sharp crash. The brain scan revealed this crash to be linked to intense hunger and strong activation of the nucleus accumbens, a region of the brain involved in addictive behaviour, reward and craving. The researchers suggest that limiting high GI foods may be one way of controlling the urge to overeat.

Meanwhile, research by Garret Stuber and his team at the University of North Carolina has shown that at least one specific neural circuit drives overeating – at least in mice. When this circuit is triggered, he believes animals eat because they enjoy it rather than because they are hungry.

Meanwhile in Bristol, Prof Brunstrom is working on a different approach to understanding overeating. His research suggests that planning what to eat before a meal may be as important as the satiety signals generated during the meal itself, even if we are not always conscious of this forward thinking. His team has developed ways of measuring the expected satiety (ES) of different foods – that is, the extent to which we perceive a food as able to stave off hunger.

“There is a large mismatch between how many calories a food contains and how filling it is perceived to be,” he says. “For instance, potatoes have a higher ES than chocolate. Very energy dense foods like chocolate are perceived to deliver less reduction in hunger.” Decisions on ES seem to be influenced by volume, with higher volume, less energy-dense foods seen as more satisfying.

It is possible to manipulate a food for ES by altering its viscosity. Drinks tend to have a low ES but are often loaded with calories, so their unthinking consumption has been linked to weight gain. On the other hand, increasing viscosity and creamy texture increased the ES value of a yoghurt drink. This could be one way of reducing the amount of energy-containing drinks consumed.

How much people eat is also influenced by factors such as the size of the packet, plate and portion, the variety of food available and the context in which it is eaten. This is well illustrated by one of Wansink’s experiments which shows that people will eat, even if they are not hungry and the food is not palatable. His team invited unsuspecting volunteers to a movie, offering free popcorn in return for answering a questionnaire. The popcorn was five days old and tasted stale. Most of the volunteers had already lunched, so they were not hungry. Yet they still ate the stale popcorn. Some were given medium-size buckets, others large-size buckets.

Those given the latter ate more (173 calories more, equivalent to 21 more dips in their bucket), even though they hotly denied being influenced by the size of the container when questioned afterwards. Wansink has run many other popcorn studies and the findings are the same – people eat more from a larger container.

SIZE MATTERS

The size issue is worth looking at in more detail. Between 1970 and 2000, the number of large sizes of food products in supermarkets increased tenfold. The spread of fast food outlets has led to the proliferation of super-size and jumbo-size portions as chains compete in the ‘value for money’ stakes. In a famous study carried out by University of Pennsylvania psychologist Paul Rozin and the French sociologist Claude Fischler in 2003, portion sizes were compared in fast food outlets, pizzerias, ice cream parlours and restaurants in the cities of Philadelphia and Paris. Of 36 meals and beverages compared, 26 had a significantly lower mass in Paris, with portions being an average of 25 per cent heavier in the American city.

To illustrate the point, Wansink invited 85 nutrition professors and graduate students to an ice cream party. On arrival, they were given either a medium or large bowl and either a medium or large ice cream scoop and told to help themselves. Those given large bowls and scoops served themselves with 53 per cent more ice cream than those with small bowls and small scoops.

This tendency to eat more from a large portion is likely because you can consume a lot of food before you see much difference in the portion size. The ‘clean plate’ perhaps gives the eater a goal, which acts as a clear signal to finish eating – only you have to do more eating to achieve this with a big portion.

VARIETY IS THE SPICE OF LIFE

Another important factor in overeating is variety. Brunstrom has carried out experiments that show how variety increases the amount of food consumed. Participants were shown images of four dishes – chicken tikka masala, spaghetti bolognese, apricot slice and lemon tart – in various combinations on a computer, and asked to manipulate the image of the second course to show how much they would serve themselves. When there was variety – when sweet followed savoury – the volunteers rated the foods as more pleasant and said they would select a bigger helping.

Meanwhile, as you head towards the office Christmas lunch or New Year’s dinner, bear in mind that psychology professor John de Castro of Georgia State University has figured out that you eat 35 per cent more if you eat with one other person than if you eat alone. If you eat with a group of seven or more, you consume nearly twice as much. This is because chatting distracts us from the food and we stop monitoring what goes into our mouths. On the other hand, speedy eating also tends to lead to overconsumption. Many studies have shown that it takes 20 minutes for the brain to act on satiety signals from the body, which is plenty of time for a second slice of pizza or a return visit to the buffet.

However, there are many tricks for thwarting the conspiracy between the brain and the environment which seems to promote overeating. For instance, at the festive buffet, put your plate down when you are chatting and put only two items on your plate at each trip to the food table. If you are shopping for crockery in the January sales, buy some smaller plates for dinner. In a restaurant, you could opt for two starters and skip the main, or maybe share a pizza or a dessert. Wansink also describes the ‘pause point’, and recommends creating interruptions in your eating – by choosing individually wrapped biscuits, sweets or chocolates, or by moving dishes of food out of easy reach. Finally, be mindful in your eating – ignore distractions, focus on the food and eat it slowly.

The general tendency to ‘clean the plate’ and eat whenever the opportunity arises seems to imply an inherent greediness in human nature. Maybe it is a throwback to our hunter-gatherer past, when people never knew when they would eat again? In those days, this behaviour had a clear survival value. In 21st Century Britain, the opposite is probably true.

**********

OVEREATING IS HARDWIRED IN THE BRAIN

The lateral hypothalamus (LH) is a part of the brain that is involved in motivational behaviours, including feeding. It’s long been known that stimulating the LH will cause a mouse to overeat. But it remained a mystery as to which particular neurones were involved, which is where we came in. We’d noted that so-called GABA neurones close by, in another region, had very dense projections into the LH, so we decided to investigate this. This region is actually an outcropping of the amygdala, which is involved in emotion, and forms a bridge to the LH.

We used a technique called optogenetics, where we genetically modified the GABA neurones we were interested in so they could be stimulated by an optic fibre implanted into the brain. In this way, we could turn the circuit on and off to see what happened to the behaviour of the mice in the experiment. They started to eat within seconds of the circuit being stimulated and continued to eat, even though they couldn’t be hungry, until we turned the circuit off. When the circuit was off, they showed no interest in food – even if they were hungry. Stimulating this circuit increases the palatability of food, rather than satisfying hunger, because the LH is also involved in behaviour that leads to a reward.

This same brain pathway is very likely to exist in humans because this is a region of the brain that’s been well conserved during evolution. So we’re now trying to set up studies to see if this behaviour is replicated in humans. Our studies underscore the fact that overeating has a strong neurobiological basis and the role of brain circuitry is very significant. This brain pathway may play a role in food consumption and eating disorders, such as binge eating, and further research may help us work out how to modify it and develop treatments.
(By Dr Garret Stuber of the University of North Carolina School of Medicine USA)

**********

CURB YOUR OVEREATING... WITH AN IMPLANT

A new pacemaker for the stomach could be the key to helping people who are unable to control their food consumption.

The vagus nerve helps regulate sensations of hunger, satisfaction and how full you feel. Surgical vagotomy, which involves cutting the vagus nerve near the stomach, was used historically as a treatment for stomach ulcers. Patients often experienced weight loss and reduced appetite as side effects. The Minnesota-based company EnteroMedics used these findings as a basis for designing its VBLOC therapy, which intermittently blocks vagus nerve signals between the brain and the stomach with a pacemaker-like device called the Maestro System. This is implanted and programmed by minimally invasive surgery and has been safely used in over 600 patients in clinical trials, producing significant weight loss.

Existing treatments for obesity – namely, diet and exercise, medication and weight-loss surgery – all have their drawbacks. EnteroMedics believes that VBLOC therapy can fill the gap and offer new hope for the 20 million obese people who would currently qualify for surgery because of their weight and complications like diabetes or high blood pressure.


By Susan Aldridge in "BBC Focus UK", January 2014, excerpts pp. 41-45. Adapted and illustrated to be posted by Leopoldo Costa.