Dieters frequently report reaching their goal weight, only to find that the pounds creep back on.
Scientists say the trick to keeping weight off permanently is to cut 300 calories from your daily food intake.
In a study presented at the European Congress on Obesity earlier this year, Professor Michael Rosenbaum described how dieters need to consume 22% fewer calories a day than someone who hasn’t dieted simply to maintain their weight (so a non-dieter could consume 1,600 calories a day and not gain weight, while a dieter of the same weight must stick to around 1,300).
Scientists say the trick to keeping weight off permanently is to cut 300 calories from your daily food intake
Dietitian Linia Patel, spokesperson for the British Dietetic Association, says: “It’s believed this phenomenon can be explained by the effect dieting has on muscles. Dieters’ muscles need fewer calories to do the same work than those of people who haven’t been on the diet in the first place.”
As we age the picture becomes even bleaker.
“Lean muscle helps the body burn a greater number of calories, but as we age our muscle mass drops along with our metabolism.”
The result is that our bodies need fewer calories to maintain our weight.
But extra calories can be burnt off through exercise – resistance training and lifting weights are among the most effective ways to build lean muscle mass.
Experts have found that slimmers need to eat less than someone of the same weight who has not dieted to stay at their new weight.
To be precise, they need to eat at least 300 fewer calories a day. This equates to a bag of Maltesers and a Milky Way – the sort of treats they were probably looking forward to enjoying after the pounds had come off.
And over the course of a week, it amounts to 15 cans of cola or 17 slices of buttered toast.
The European Congress on Obesity heard that several quirks of biology combine to create a “perfect storm” that makes it all but impossible to keep lost weight off.
The calorie counts come from Professor Michael Rosenbaum, of New York’s Columbia University, who has monitored dieters for years at a time.
The men and women are taken into hospital and put on a strict diet to shed 10% of their weight.
They then try to stay at that weight. Test carried out before and afterwards have revealed the secrets of their success – or failure.
Experts have found that slimmers need to eat less than someone of the same weight who has not dieted to stay at their new weight
Prof. Michael Rosenbaum said: “The number of calories you are going to have to eat to maintain that weight loss falls by 22%.
“That’s 300 calories or more a day less than someone who looks exactly like they do.”
What is more, his studies suggest that the effect does not wear off, with an ex-dieter having to eat hundreds of fewer calories a day for years to come if they are to stay slim.
The conference in Lyon heard that the phenomenon can largely be blamed on the effect dieting has on muscle.
In slimmers, muscle uses fewer calories to do its work than in someone else of a similar weight who has not dieted.
Changes in hormones, metabolism and appetite also play a role.
Prof. Michael Rosenbaum’s studies also show that after dieting, the areas of the brain that perceive food as rewarding are more active, while those that generate feelings of restraint are less so.
And former dieters have to eat more to feel satisfied, but think they have eaten less.
He said: “You are creating the perfect storm for weight regain – energy expenditure is down and desire to eat is changed in ways that favor regain of lost weight.
“Weight loss is a relatively brief therapeutic intervention, but trying to keep the weight off requires a lifetime of diligent attention.”
A new study findings presented at the European Congress on Obesity suggest that older obese men could shift excess weight by taking testosterone supplements.
In a study, hormone-deficient men were given testosterone supplements in a similar way to HRT for older women.
Men lost an average of 16 kg over five years when testosterone levels were increased back to normal.
But experts warn that supplements may not be the answer due to possible risks of prostate cancer and heart disease.
Prof. Richard Sharpe from the University of Edinburgh Centre for Reproductive Health said: “The notion that this is a quick fix for obese older men is, as always, simplistic. It is far more sensible and safer for men to reduce their food intake, reduce their obesity, which will then elevate their own testosterone.”
Men lost an average of 16 kg over five years when testosterone levels were increased back to normal
The findings announced at the conference also suggest that raising testosterone levels could reduce waist circumference and blood pressure.
Dr. Farid Saad, lead author of the study said: “We came across this by accident. These men were being given testosterone for a hormone deficiency – they had a range of problems – erectile dysfunction, fatigue and lack of energy.
“When we analysed the data we found that every year, for five years, they had lost weight. It may be that the increased testosterone restored their energy levels and led to a behavioural change of being more physically active.”
However, experts remain dubious. While some experts have linked low testosterone levels to a male “menopause”, with symptoms including changes in sleeping patterns, poor concentration, feeling worthless and anxiety, others have found to have no such link.
The study looked at 115 obese men aged between 38-83 years with low testosterone levels. They were injected with the hormone every 12 weeks to increase levels. The research, paid for by Bayer Pharma, a manufacturer of testosterone replacement therapy, found no increased risk of prostate cancer, a side-effect found in other studies.
The relationship between obesity and testosterone appears to be a vicious cycle. There are numerous studies showing that obesity, in particular abdominal obesity, is associated with reduced testosterone levels in men and a reduction in muscle.
With ageing, especially beyond 40-50 years, testosterone levels tend to decline slowly, which may predispose to abdominal obesity which will then further lower testosterone levels.