Low carb, high fat diets don't work better than traditional balanced diets, according to a Stellenbosch University study.
Low carbohydrate diets, such as the diet that Tim Noakes from the Sports Science Institute of South Africa at the University of Cape Town advocates, result in no more weight loss than “recommended balanced diets”, a Stellenbosch University study released on Wednesday night has found.
The study, published in online medical journal PLOS ONE, pooled the results of 19 clinical trials conducted in high-income countries, and measured weight loss and heart disease risk factors such as blood cholesterol levels. Researchers monitored 3 209 overweight and obese participants for periods of between three months and two years.
In each of the trials, the participant’s calorie intake was controlled, in other words, those on low carbohydrate diets consumed the same amount of calories as those on “balanced diets”.
Researchers defined a balanced diet as one that “reduces energy intake by guiding healthy food choices and decreasing portion sizes, while keeping the carbohydrate, protein and fat within the recommended ranges of intake”. Balanced diets include plenty of vegetables, fruit and unrefined carbohydrates such as rice and oats, and emphasise vegetables and fish fats and oils instead of animal fats.
By contrast, a low carbohydrate diet such as the “Banting” diet that Noakes has been promoting eliminates food with high quantities of carbohydrates, such as potatoes, rice, bread, cereal and pasta, and replaces them with food that has a high fat content, such as fatty meat, cheese, coconut oil and certain types of nuts.
Popularity of Banting diet
Noakes’s ideas have rapidly gained popularity in South Africa and he has reported people losing as much as 80kg in seven months after following his diet. Earlier this year, he co-authored a book titled The Real Meal Revolution, with recipes for the Banting diet, that sold out within weeks of hitting the shelves. Social media platforms such as Twitter and Facebook have been abuzz with South Africans boasting of instant weight loss.
But many medical scientists consider Noakes’s diet controversial and view it as a potential health risk owing to its high fat content. Noakes has been heavily criticised for promoting eating habits for which many say he lacks scientific evidence and for which he has not attempted to conduct clinical trials.
But now, Stellenbosch researchers say, they’ve got evidence to “clear up the misperception” that low carbohydrate diets make you lose weight faster.
“This systematic review shows that when the amount of energy [calories] consumed by people following the low carbohydrate and balanced diets was similar, there was no difference in weight loss after three to six months and after one to two years in those with and without diabetes,” said lead researcher Celeste Naude from the Centre for Evidence-based Health Care at Stellenbosch University’s faculty of medicine and health sciences.
But Noakes has strongly objected to the study, saying “if you control the calories [when comparing the two types of diets] you falsely advantage low fat diets, as people on low fat diets with high amounts of carbohydrates are almost always hungry”.
“The reason why people lose so much more weight on low carbohydrate diets is because they lose their hunger [fat intake is known to reduce hunger leading to less food intake] and that’s key,” Noakes told the Mail & Guardian.
“Low fat diets are unsustainable because as soon as you eat carbohydrates you stimulate your appetite – you can only sustain that for a period of time, like these clinical trials do, but then you go back to overeating after a year or so.”
According to Noakes, the clinical trials analysed in the Stellenbosch study did not take into consideration that people (who are not participating in trials) are “free living human beings” who are rarely driven by calorie intake.
“If you control the calories, of course you won’t see a difference in weight loss. But that’s not how people live – they eat according to how hungry they are,” he said.
What is low carb?
Noakes and the researchers also differ on the definition of a low carbohydrate diet: Noakes considers it to be a diet with as little as 25-50g of carbohydrates a day, while the Stellenbosch researchers defined it as one in which the carbohydrate content is less than 45% of the total diet. “That’s more than 200g [four to eight times more than Noakes’s amount] a day – far too much.
People who are obese should not eat more than 50g a day,” Noakes said.
Two in three adults are overweight or obese, according to the Stellenbosch researchers. Heart disease and diabetes, which scientists have shown have a far higher prevalence in overweight people, are also major problems in South Africa, with deaths owing to those conditions being twice that of deaths in the United States.
Long-term studies have found that the risk of such lifestyle diseases is reduced when a person follows a balanced diet with low fat dairy products, lean meats and vegetable oils, while a high fat intake traditionally has been linked to an increase in heart disease.
But several leading researchers have questioned this premise recently, with international news magazine Time leading its coverage on June 23 with a story titled “Eat Butter. Scientists labeled fat the enemy. Why they were wrong”.
According to Noakes, researchers in Time “have been saying what I’ve been saying for four years. In 30 years it’s gone from saying let’s eat low fat to saying, no we were wrong.”
But Naude emphasises that while the effects of low carbohydrate diets on health over the long term remain unknown, most research studies up until now have shown that “the dietary pattern and food choices promoted with a low carbohydrate/high fat diet are not well aligned with healthy dietary patterns and food choices known to, along with a healthy lifestyle, reduce the risk of diseases like heart disease, stroke, diabetes and cancers”.
According to the Stellenbosch researchers, improving the diets of South Africans is an important step in preventing and managing obesity, heart disease, stroke and diabetes. “There are a few longer term studies that suggest an increased risk of death and heart disease with low carbohydrate diets, but more research is needed before more conclusive decisions about this can be made,” Naude said.