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 But even "fad" diets can lead to a slimmer, lighter
New Year for those whose resolve remains robust, according to
doctors and nutritionists analyzing them.
Gathering for a London conference to review evidence behind popular
weight loss diets — at just the time of year when slimming ideas are
in peak demand — specialists concluded that food fads such as the
hunter-gatherer "Paleo" plan or the 5:2 diet can deliver. But it's
hard work.
"If it was easy, our species would have died out years ago. As
humans we have a default to eat," said Gary Frost, a professor and
chair of nutrition and dietetics at Imperial College London.
The results of that default are looming large in a global "wave of
obesity", he said.
According to the World Health Organisation, worldwide obesity — defined as having a body mass index of more than 30 — has nearly
doubled since 1980. The latest global figure is that in 2008, more
than 1.4 billion adults were overweight.
WAVE OF OBESITY
According to the U.S. Centers for Disease Control and Prevention,
almost 36 percent of American adults are obese and almost 70 percent
are either obese or overweight. In Britain, a government health
study predicts 60 percent of men, 50 percent of women and 25 percent
of children will be obese by 2050.
Against this background, experts say the search for effective diets
must always take account of how easy it is for people to understand
and follow, and how likely they are to abide by its restrictions.
Michelle Harvie, a research dietician from the Genesis Prevention
Centre at Britain's University Hospital of South Manchester, said
that on this front, fasting diets — sometimes called intermittent
diets — can be successful.
"Energy restriction is difficult to maintain over the long term and
people tend to find it easier to follow a diet with intermittent
energy restriction," she said.
She said that while a regular weight loss plan might require the
dieter to take in 25 percent fewer calories, intermittent diets may
suggest two days of a 75 percent calorie cut interspersed with five
days of normal healthy eating.
But the key to these diets — such as the 5:2 diet in which followers
eat as little as 400 calories on two "fasting" days per week — is
that dieters won't succeed if they "pig out" and eat whatever they
want on non-fasting days.
Harvie's research shows those who succeed in losing weigh on these
diets find the fasting days lead them to also have a lower food
intake on normal days — leading to lower calorie intake overall.
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HUNTING FOR FOOD
Mark Berry, head of plant biology and biochemistry at the consumer
company Unilever's research and development unit, says there are
also positive signs in data from studies of "Palaeolithic" or
stone-age diets — plans designed to mimic the diet of
pre-agricultural hunter-gatherers of that era.
A sign of its current popularity is that "Paleo
diet" was one of the most "Googled" terms of 2013. The idea is based
around foods that can be hunted, fished or foraged for — meat,
seafood, eggs, nuts, seeds, fruits and vegetables.
Berry said his research showed little impact on glucose response in
the body in people eating a Palaeolithic diet, but did find a
significant impact on hormones that signal satiety and tell the
brain the eater is full.
Alexandra Johnstone of the Rowett Institute of Nutrition and Health,
who has been looking into high-protein and low-carbohydrate diets
such as the Atkins diet, said these also had a significant impact on
fullness feelings — giving them the potential to help dieters
control appetite and lose weight. "The high satiety
effects of increased protein in the diet seems to be a contributing
factor to the success of high-protein, low-carbohydrate diets," she
said.
Johnstone cited data showing the amount of weight lost on
high-protein diets is around double that lost on a comparable
low-fat diet at the six-month mark.
But there is little difference in weight loss after one year, as
dieters often lose momentum and their resolve to slim down fades.
"There's no magic bullet," she said.
Judy Buttriss, head of the British Nutrition Foundation, said the
evidence for popular diets was clearly nuanced. While there are
several that can be used as tools for effective weight loss and
maintenance, she said "there's currently no evidence that one is any
better than another in the long term".
(Editing by Sonya Hepinstall)
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