Women find it more difficult to follow a diet than men because they are biologically programmed to have less self control when it comes to appetite, a study into how the brain copes with food craving suggests.
An innate difference between the way men and women are able to deny themselves the pleasure of food could explain why women find it more difficult than men to lose weight and are more likely to be obese. In Britain 23.1 per cent of men are obese compared with 24.8 per cent of women.
Scientists believe that men are able to voluntarily inhibit their internal cravings for food more effectively than women, probably because evolution has honed the female body – and mind – to absorb as many calories as possible in readiness for pregnancy and lactation.
"It's a very interesting observation but we don't really know why men are better than women at inhibiting their appetite," said Gene-Jack Wang, of Brookhaven National Laboratory in Upton, New York, who led the study. "We have seen in clinical studies that men following a diet are able to lose about 10 per cent of their weight on average over a three-month period, whereas women manage a decrease of only about 5 per cent. We need to understand which areas of the brain are involved in this difference between the sexes."
The study, in the journal Proceedings Of The National Academy of Sciences, focused on the mechanism in the brain that controls appetite by suppressing food cravings. The researchers subjected 23 non-obese volunteers to a 17-hour period of fasting followed by the sight and smell of their favourite food, which they were only able to savour without eating.
Each of the 13 women and 10 men were asked to suppress their cravings through "cognitive inhibition" – self control – while the activity of their brains was being monitored by a positron-emission tomography (PET) scanner, which monitors how the brain uses glucose.
While the starved volunteers were subjected to the sight and smells of their favourite foods, such as bacon, egg and cheese sandwiches, cinnamon buns, pizza, hamburgers, fried chicken, brownies and cake, the scanner monitored which regions of their brains were most active.
When the volunteers were exposed to their favourite food, parts of the brain involved in emotional regulation, conditioning and motivation "lit up", indicating they were stimulated by the food. But when each person was asked to suppress these thoughts and use self control to inhibit cravings, only the men's brain scans showed a significant reduction in activity in the presence of food.
"We tried to understand how you can reduce food stimulation so we designed a study that asked people to use their brain power to reduce the stimulation of food, to reduce their craving for food – using real food," Dr Wang said. "Even though the women said they were less hungry when trying to inhibit their response to the food, their brains were firing in the regions that control the drive to eat.
"In contrast, men's brain activity decreased with their self reports of hunger during the scan when they were asked to keep hunger in check. This may indicate a gender difference in the ability to perceive and respond to internal body signals."
Such differences may explain why women have a greater tendency than men to overeat when tempted by tasty food or under emotional distress, Dr Wang said.
"This decreased inhibitory control in women could be a major factor in the differences in the prevalence of obesity and eating disorders, such as binge eating, between the genders, and may also underlie women's lower success in losing weight while dieting when compared with men."
Sex hormones, namely oestrogen, are known to affect appetite, food intake and fat distribution, but the scientists did not take into account how hormones vary in women during their monthly cycle – the next stage of research will include that data.
Women have proportionately more body fat than men, believed to serve as a store of energy for pregnancy and lactation. Dr Wang said that during human evolution it is feasible that appetite suppression would have been more dangerous for women than men, which is why women find it harder to suppress a desire for food.
The level of obesity is only slightly higher in British women than men, but it rises in some ethnic groups, such as black African women (38 per cent); black Caribbean (32 per cent) and Pakistani women (28 per cent).
'If women thought more about themselves, it would be easier to lose weight'
Dr Ian Campbell, Founder, National Obesity Forum
Women do generally find it harder to lose weight, possibly because they're not as adept at suppressing appetite, for two reasons. First, men are more single-minded: when they focus on something they really focus on it, whereas women are more likely to think about several issues at once, often in relation to their family. Second, oestrogen in women increases appetite. When women go on the Pill they put on weight and it's possible this is related to a failure to suppress appetite.
Linda Blair, Clinical psychologist and author of Straight Talking
We know women are able to think of more things at once. I guess that means if men get distracted by anything, that occupies their brains, whereas women will quickly return to thinking they are deprived of food. Women often lose weight for others. If we thought more about ourselves it would be easier to retain the motivation to lose weight.
Vanessa Feltz, Broadcaster and sometime dieter
I find the conclusions of this research appalling. The idea that women are shallow, flimsy, frivolous, incapacitated characters is nonsense – as if we find it fantastically hard to lose weight. If you look back at all the credit crunches, famines and times of austerity to see who has foregone food for someone else, it's women. Think of the mothers who sacrificed the choicest morsels on the dessert tray to ensure their children eat. It's not women who are incontinent. Men are sexually incontinent, completely incapable of suppressing their appetites. On the contrary, we women are at the mercy of our hormones.
Heather Caswell, British Nutrition Foundation
It is important to consider the fact that this study was only very small (using 23 people); further, the hunger response in humans and control of food intake is an area that is not yet fully understood. It is also important that women do not think this means they will not succeed if they attempt to lose weight through food restriction – many women who attempt to diet do so very successfully.
Slimline Vegas: Four stone in a year
Johnny Vegas, the generously proportioned comedian famed for his love of junk food and Guinness, has lost more than four stone after suffering from gout.
Vegas, 37, has suffered from the disease for years and has occasionally been forced to cancel gigs after severe bouts. He began dieting last year and is now close to 13 stone.
Gout is caused by the build-up of acids around joints and tendons, and can lead to excruciating, burning pain and swelling. Eating protein-rich foods and drinking alcohol can both exacerbate the condition, prompting the comedian's decision to give up his beloved pies, kebabs and beer in favour of a new low-fat diet.
He said: "There's no big deal behind it, I've just been eating sensibly and I've done it for health reasons. I didn't have any issues with my size. It's been a really gradual thing, but I had a bit of time off to write, so when I turned up back on the telly, people suddenly noticed I had lost weight and thought it happened overnight."