Image of dissected bone

Credit: Radius Magazine

When an overweight person starts a lifestyle program to lose weight, they exercise, eat well, and soon the kilos are falling off.

In the beginning, everything goes well ... and then they hit a brick wall. The weight refuses to budge. “It’s what I call ‘the famine reaction’. It is as if the body is saying, ‘This is no good. I’m not going to let you lose any more weight.’ It is the body’s response to protect us,” says Associate Professor Amanda Sainsbury-Salis, senior research fellow at The Boden Institute of Obesity, Nutrition, Exercise & Eating Disorders.

That protection mechanism is very useful in times of food scarcity, or in the case of sickness. It can even mean the difference between survival and death. Unfortunately, in times of plenty, when you are trying to shed a few kilos of unwanted weight, it’s not so helpful. “The body defends this higher than ideal body weight and thinks it’s normal,” says Sainsbury-Salis. This ‘normal’ weight is referred to as the set point, and in some overweight individuals, the set point has been increased.

Just as the famine reaction stops us losing too much weight, there is a reverse process which protects people from gaining too much weight: the fat brake. Sainsbury-Salis quips that the fat brake has reliably been observed in medical students, “because they are frequently used in over-feeding experiments. “If you feed these people around 4000 kilojoules in excess of their daily energy requirements, their metabolic rate will rev up, they’ll feel warm, they start fidgeting and they lose appetite.”

In fact, most people have this fat brake, but it may be the case that eating too much for too long, eventually wears down the ‘brake lining’. “Animal research has shown that if you feed rats a diet high in fat and high in sugar over 20 weeks, the fat brake mechanism becomes defective. In humans, we don’t know if long-term exposure to a diet high in processed food causes permanent damage to the fat brake.”

The progression of weight loss varies for different people. “Some will lose a kilo or more a week for 40 weeks before they experience the famine reaction. They start to get hungrier, their metabolic rate falls, there is a change in hormones with an increase in hormones which tend to make the body store fat. Then there are other people who hardly lose any weight at all before the famine reaction strikes and they become ravenously hungry.”

There would be an advantage in predicting which people will fall in the latter category. For these, there may be little efficacy in dieting. They are likely to need pharmacological intervention or bariatric surgery; not a decision to be taken lightly. Sainsbury-Salis is keen to look at how we can attenuate or block the famine reaction. She hopes to develop bio-markers so we know when the famine reaction is hit. She says that it’s not enough to simply ask the dieter if their hunger is increasing. “Hunger is subjective. We can feel hungry when we are passing a food outlet. These biomarkers will be from saliva or urine or blood. When we know we’re having a famine reaction, then maybe it’s time to switch from weight loss to weight maintenance for a while. It will also be helpful to tell people there’s a reason why they are feeling hungry.”

She’s also looking at a way of decreasing the intensity of the famine reaction. “If people stop dieting and eat more to maintain their weight – not enough to increase or decrease weight - after a few weeks, the effect of the famine reaction may be reduced. Some studies do show this so there is a glimmer of hope.”

She is suggesting that instead of going on a diet and sticking with the regimen until you reach your ideal weight, it may prove more effective to take breaks along the way, allowing the body to recalibrate its set point. The biomarkers will let dieters know when it’s time to ease off. In dieting, it seems, constant energy restriction may not be so desirable after all. “There is research that suggests you can get an attenuation of the famine reaction after two weeks of weight maintenance, however, I suspect that it will take a lot longer for people who have struggled with their weight for a long period of time. Maybe it will take months,” says Sainsbury-Salis.

“The bio-markers that show when the famine reaction is turned ‘on’, could also tell us once it is turned ‘off’ and the time is right to return to dieting.” For Sainsbury-Salis, weight loss is about how we can get all the tools we know to work together. We know that exercise is good for us and definitely helps with weight maintenance after weight loss. With physical activity you have a better chance to keep the weight off. In studies with obese rats, after weight loss they ate more and regained their weight. Their bodies were defending the set point. Then exercise was added. They were able to maintain their weight loss more effectively, not because the exercise was burning calories but because it reduced their drive to over eat.

“We know that exercise helps people with weight management, and this research with rats provides clues about how it works. Exercise blunts the famine reaction by reducing hunger. While exercise certainly speeds up weight loss, it is most important after losing weight. Many people can lose weight with dieting alone, but the crunch time is when the weight is off. It’s then that exercise is absolutely essential for preventing weight regain. We encourage people to gradually increase their level of physical activity while they are losing weight, so that once they reach a healthier weight they will be ready for the levels of physical activity required for long-term weight maintenance. It’s a lot, but you don’t have to be doing it all when you start to diet.”

One of the ways that Sainsbury-Salis is looking at blocking the famine reaction is with fast weight loss with severe energy restriction. “It seems counter-intuitive, but there is evidence that losing weight quickly on a very energy-restricted diet reduces the famine effect. We want to compare fast and slow dieting.”

She is recruiting post-menopausal women for a trial* which will start this year. “We are trying to reduce the variability in outcome measures and the menstrual cycle has effects on the parameters of the famine reaction.”

Surprisingly, she says that those participants who are on the semi-starvation diet are unlikely to suffer hunger pangs. “On really low energy diets, people report that they don’t feel hungry. Hunger is repressed while energy intake is restricted, and only kicks in when the diet is over.”

Sainsbury-Salis knows from first-hand experience how difficult losing weight can be. “I lost 28 kilos and kept it off for 15 years. I’ve been in that obese state. I’ve experienced losing just 5 kilos with a sensible balanced diet and feeling ravenous even though I was still obese. The ‘experts’ sent me off to get psychological help for over-eating. Maybe it was just my famine reaction.”