What would make you put on the most weight – eating 5000 calories a day on a high fat/low carb diet or 5000 calories on a high carb/low fat diet? To a conventional nutritionist this will sound like dietary version of the old school-days trick question: Which is heavier a ton of bricks or a ton of feathers? That’s because the units are the same in both cases– whatever the calories come from they are still calories, just as the bricks and the feathers both weigh a ton.
But according to an article of mine in the Daily Mail today, calories aren’t like tons of feathers and bricks. Instead while calories are indeed identical on the plate, once they start interacting with the complex biochemistry of our bodies they can have very different effects on weight.
If that’s true then dieticians’ advice for the last 40 years that weight loss is simply a matter of restricting calories wherever they come from been damagingly wrong The article is about a dramatic challenge to the “calorie-is-a-calorie” hypothesis posed by a personal trainer from East London called Sam Feltham who wanted to test if eating 400 grams of fat a day really would pile on the pounds.
After three weeks on the high fat diet, he built up a calorie surplus that conventional thinking predicted would result in a weight gain of about 7 kg (16 pounds). In fact he put on just over a kilo and actually *lost* an inch from around his waist.
Surprised and delighted he then tried the same thing with a high carb diet and the results were very different – a weight gain of more than seven kilos and an extra three inches around the middle. Details of what he was eating, his exercise routine and the calorie excess are all available in the Mail article.
It’s the insulin that matters
The brief explanation of why calories are not equal is because cabs raise insulin and fat doesn’t. This matters because fat eaten when glucose and insulin are raised on a high carb diet is more likely to be swept into storage than the same amount of fat when insulin is low on a low carb diet. What’s more high fat makes you less hungry so you eat less than you do on high carbs.
What’s remarkable, given that the benefits of a low fat diet have been dietary lore for 40 years, is that evidence strongly suggesting it was a mistake date back even further. Dr Michael Eades, a long time campaigner for the benefits of the low carb diet, has described two early experiments that showed clearly that the low carb diet was certainly a far more pleasant way of losing weight than the low fat approach.
The first was done in 1944 by Ancel Keys – that man who linked raised cholesterol with heart disease. He was trying to discover what would be happening to the starving millions in Europe as the war was coming to an end. In a famed experiment at Minnesota University he put 36 male volunteers onto a restricted calorie, high carb diet of about 1500 calories a day – carbs 225 gms, fat 30g and protein 100g.
The most striking, but not surprising, finding was that the subjects hated it. They obsessed about food, they were lethargic, cold and depressed.
Eades compares this with what happened to another group of volunteers in the late 1960s that was put on a high fat diet – carbs 67g, fat 105g and protein 83g – by another famed nutritionist Dr John Yudkin. The aim of the two-week study was to check for nutritional deficiencies and the volunteers were allowed to eat as much high fat foods as they wanted.
There were two striking results. First, even though food was not restricted, the subjects spontaneously reduced their intake to almost the same amount as Key’s miserable volunteers. Secondly they enjoyed it, reporting increased well-being and decreased lassitude.
Since then evidence for the benefits of low carbs has accumulated and usually along with vituperative attacks from the low fat believers. Yudkin’s book Pure White and Deadly warning against the dangers of sugar and in praise of fat was savaged as were Robert Atkins’s books two decades later. Both fit better with the emerging consensus.
Faith of the believers
Gary Taube’s masterly Big Fat Lie traces how low fat triumphed and meticulously detailed its scientific shortcomings. Just one paper of hundreds challenging the low fat dogma came out earlier this year entitled A New Look at Carbohydrate Restricted Diets. “Recently published research seriously questions the dangers of dietary saturated fats,” write the authors “and also any potential health benefits of the low fat diet.”
Yet the faith of the believers remains unshaken, while at the same time they insist they are following an evidence based approach. A recent Inside Health program chaired by Mark Porter was considering the benefits of the 2-days-off 5-days-on diet. There was nothing special about it asserted Dr Margaret McCartney: “No matter what diet you look at it is going to be about reduction of calories.”
Perhaps the time has come to distinguish between dietary feathers and dietary bricks.