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Study Reveals 'Most Effective Diet'
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Scientists at Aberdeen’s Rowett Research Institute have shown that a high
protein, low carbohydrate diet is most effective at reducing hunger and
promoting weight loss, at least in the short term.
Healthy, obese men were given two different diets during their stay in the
Rowett’s specialised Human Nutrition Unit. Both diets had a high protein
content (30% of total energy value of the diet) but they differed in the amount of
carbohydrate: One diet was low in carbohydrate (4%) and the other contained
a moderate amount of carbohydrate (35% total energy value).
“Our volunteers found both diets to be equally palatable, but they felt less
hungry on the high-protein low-carbohydrate diet compared with the diet which
contained high-protein but moderate amounts of carbohydrate,” said Dr Alex
Johnstone, the Rowett’s weight-loss expert who led the study.
“Weight loss during the two four week study periods was greater on the high-
protein low-carbohydrate diet, averaging 6.3 kg per person, compared with
4.3 kg on the moderate carbohydrate diet,” said Dr Johnstone.
An important part of this study was to unravel the physiological mechanisms
behind this type of diet. It is known that when people eat low carbohydrate
diets, within a relatively short time their body has to switch from using glucose
as a fuel to using something different called ketone bodies. Ketone bodies are
appetite-suppressing and they may have an effect on the appetite centres in
the brain. It’s also well known that protein itself is very good at making people
feel full-up.
“In this study, we showed that on the high-protein low-carbohydrate diet the
volunteers became ketogenic within 1-2 days of starting this diet and so it
may be that high-protein, low-carbohydrate diets are particularly effective
because of the combined effect of the protein and the ketone bodies,” said Dr
Johnstone.
“We showed that the volunteers on the ketogenic diet reduced their energy
intake without increasing their hunger and this was a very important factor in
their ability to stick to the diet.”
However, Dr Johnstone sounds a note of caution about her findings.
“A paper published last year from the same study showed that low
carbohydrate diets may have consequences for the health of the gut by
dramatically reducing the numbers of particular types of bacteria. So we will
be looking in more detail at the complex way in which we respond to changes
in our diet before we can say whether low-carbohydrate ketogenic diets are a
suitable tool for everyone who wants to lose weight.”
When the phase of the study which involved the volunteers finished in October
2004, it attracted considerable interest because of its celebrity volunteer,
Cameron Stout, who lost just over 12 kg during his nine week stay at the
Rowett Institute. At the time, Cameron mentioned his surprise at not feeling
hungry during the study and said he had adjusted to eating smaller portions.
How does he feel now, three years later?
“I had a great experience with the nutrition study at the Rowett. The food was
excellent and the staff looked after us very well. Because I have such an
irregular lifestyle I don’t find it easy to stick rigidly to all that I learnt while I was
at the Institute, but I try to make an effort most of the time. For me it was mainly
about breaking bad habits – and I guess we all have food vices we need to
deal with!” said Cameron.
The study appears in the American Journal of Clinical Nutrition.
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