Just how accurate and informative was BBC2’s Horizon program on Wednesday that aimed at scientifically answering the question: which is more deadly: Eating lots of sugar or lots of fat? The format was to feed two doctors who were also identical twins – Alex and Chris – unlimited amounts of one or the other. Alex got a low carb/high fat diet while Chris followed the traditional low fat/high carb diet with added the sugar.
Officially the result was an undramatic draw. Neither is to blame for making us sick and overweight individually. It’s only when they join forces do the twins become evil – think ice cream or glazed donuts. In fact the program’s headline message was the familiar, but still welcome, advice to avoid most processed food.
Dieticians don’t understand the diet
But few viewers will have been left in any doubt that as a lifestyle choice the low carbohydrate diet is a bad thing. This is a highly misleading conclusion for reasons that will become clear. A charitable explanation would be that those setting up the experiment didn’t understand how this diet actually works or how the body responds to it.
Less charitably it might be that the 40-year-old low fat diet lobby is very influential and has been under considerable attack recently from those who point out that demonising fat isn’t supported by good evidence and that there are good reasons why feeding people a heavy diet of carbohydrates can lead to metabolic problems.
So HealthInsightUK asked some of our expert contacts and contributors to give us their response to the program.
Hannah Sutter writes…
No one would want to be on Alex’s diet, certainly not any of the people I know who regularly eat like this and report great results. The aim of going on a really low carb diet is to reach the point where the body switches from using glucose (from carbohydrates) for fuel to being able to burn fat in the muscles. Fat gets released from the fat stores (why this diet is good for losing weight) which the liver uses to make compounds called ketones that the brain can use for energy.
Alex did poorly compared with Chris on two key trials – a test of his thinking skills and how well he could sprint up hill on a bike. He lost more weight at the end but half of that was supposedly protein that his body had turned into carbohydrates to make up for the ones missing in his diet.
But Alex wasn’t on a ketogenic diet which meant that these supposedly “scientific” comparisons were deeply misleading.
To drop your carbs low enough be become ketogenic you have to limit your cheese intake because it has quite a lot of sugar. But Alex was given unlimited diary by the dietician Amanda Ursell. This is no surprise as Ms Ursell has no expertise in low carb high protein ketogenic diets.
Wrong and misleading
Someone who understood the ketogenic diet would also have increased the amount of protein available because it is well known that the body breaks down muscle for carbohydrate unless there is enough protein in the diet. So the starting point was not only wrong but misleading. We were not comparing two bodies being fuelled by different energy sources. If Alex had been producing ketones he might well have had the energy available to power his brain in the thinking test.
This fundamental misunderstanding about low carbs and ketones showed up most clearly in the cycling test. A number of clinical trials have shown it takes about 6 weeks for a body, to become ketoadaptive, (ie to perform as well on fats as on glucose) and you need to exercise in that time help the process. Not only was Alex probably not ketotic, but had only been on the diet for a few weeks and had done no exercise.
But even a properly ketoadapted athlete would have used glucose as a power source for a sprint because the ketogenic diet comes into its own in endurance sport. The external expert was fundamentally wrong when he told the twins you cannot burn body fat for energy. This is exactly what happens when you are in ketosis and my top athletes use fat burn to deliver top results.
The tests, along with the rest of the program were more about entertainment than proper science. So it was particularly infuriating when Alex, on camera, dismissed Dr Robert Lustig’s “Insulin Hypothesis” that explains the toxic nature of sugar, for not being supported by robust science. Having read his book I can say that it is a lot more robust than this naff, poorly constructed and deeply misleading study for the BBC.
We eat less and still we are fatter
Equally unimpressive was Dr Susan Jebb who was asked to comment as an expert. In her calm and very assured manner she tells the audience that her studies have shown that no extreme diet makes any difference to health and that to lose weight we should simply eat a little less and move a little more.
It sounds convincing but Dr Susan Jebb has never carried out a proper study into a high fat ketogenic diet and she believes that saturated fats cause heart disease, even though the evidence is very weak. What’s more I have yet to find any published peer reviewed clinical trial that shows exercise has any influence on serious weight loss.
The icing on this high carb cake of misinformation is that there is no peer reviewed published clinical trial that shows that eating a bit less will have any real impact on serious weight loss. In fact, according to official government statistics, as a nation, we eat less today and do more exercise than we did 10 years ago but we are fatter than ever.