Horizon: Sugar v Fat

A summary for those who missed it and the missing facts for those who saw it

Sugar v Fat
Dr Xand and Dr Chris Van Tulleken

Some of you may have tuned into see BBC’s Horizon: Sugar v Fat which looked at the difference between a high sugar diet and a high fat diet. It was based on a contrast between the US philosophy which treats sugar as a toxic substance and the UK philosophy which still sees fat as the culprit behind obesity.

Cunningly they set about by conducting an experiment where two handsome doctors (this was irrelevant and I don’t think they were GPs, rather PHDs of some kind) who were identical twins (this is the more relevant part) restricted their diet to adhere to two basic rules. Twin 1 (we’ll call him Dr Sugar) was to survive on a diet solely of carbohydrates which contain no fat. This encapsulates sweets, pastas, oats, potatoes and basically anything which we would call carbs or sugary treats. Twin 2 (let’s call him Dr Fat) was to live for a month on a diet of only fatty foods which contain virtually no carbohydrates. This encapsulated meats, cheeses, dairy products but no vegetables or carbohydrates. They were both allowed to eat as much as they desired as long as they stuck to the above rules. The twins were closely monitored to follow changes in their body composition, alertness, fitness performance, cholesterol levels, blood sugar levels and appearance.

This experiment was backed up with interviews from various other researchers who had conducted similar experiments using rats as subjects.

What did they find?

The following is a summary of the findings with specific reference to the twins:

  • In one sitting Dr fat was likely to consume fewer calories than Dr Sugar who was able to polish off almost 50% more calories than Dr Fat.
  • Dr Fat became fuller more quickly and was full for longer periods of time between meals.
  • Dr Sugar was more alert, able to think more quickly and concentrate better.
  • When asked to do a physical task Dr Sugar outperformed Dr Fat when fueled by their respective energy sources. The task was a cycle at maximum speed up Box Hill.
  • Dr Fat lost approximately 3.5kg of body mass, 2kg of which was muscle and 1.5kg of which was fat.
  • Dr Sugar lost 1kg of with a 50/50 split between fat and muscle.
  • From this it appeared as though they were saying that a high fat diet resulted in a disproportionate amount of muscle loss, which they concluded is unhealthy.
  • Dr Fat developed a reduced ability to deal with high sugar levels due to a lack of insulin production (a symptom associated with type 2 diabetes)
  • Neither of them particularly enjoyed eating the food they were allowed to eat.

Other nuggets of info provided by the other researchers:

  • When eating a diet of mainly fats, rats consumed a reasonable quantity of food and gained no weight.
  • When eating mainly sugars, rats consumed a reasonable quantity of food and gained no weight.
  • When eating foods that were a balanced combination of fat and sugar the rats grazed constantly and gained a significant amount of weight.
  • They summarized that foods which were a 50/50 mix of fat and sugar were the most moreish and resulted in the most weight gain as we tend not to stop eating them once we’d had enough.

What they didn’t tell you:

  • How much exercise they were doing whilst conducting this experiment (I got the impression it was none)
  • That the body uses muscle as a fuel in situations where calorie intake is reduced to less than is needed to survive (starvation) and the muscles aren’t being regularly used. This is to make the body more efficient. If muscle, which uses up fuel to survive, isn’t being used, it is logical to shed the muscle by using it as a fuel source. This means that going forward the body will burn less fuel and can survive for longer where calories are in short supply.
  • That carrying out muscular workouts limits muscle loss in starvation situations as the body assumes that the muscles need to be retained as much as possible. In this situation fat would be the main source of fuel for survival, resulting in fat loss and muscle retention.
  • Who was the fitter person at the start of the experiment (this would have had an effect on finding out who was the fastest cyclist up the hill).
  • The fact that different energy sources fuel us for different intensity activities.  Dr Sugar was quicker up the hill on the bike because when performing physical activity at a moderate intensity, carbohydrates are the body’s preferred fuel source. Fat cannot be converted into usable energy quickly enough to supply a sufficient amount of fuel for those activity types. However, should the Drs have attempted a 100km walk, it may well have been Dr Fat who came out on top as fat is a preferable fuel source at lower intensity activities. For more info on this see my previous post: The Truth About Fat Burning
  • How much they each weighed when cycling up the hill-this would have had an effect on the ability to climb the hill-although based on the above statement it is always likely that Dr Sugar would have won irrespective of body weight.
  • How much, if any, alcohol was consumed during the challenge. Presumably Dr Sugar would have been allowed alcohol but Dr Fat would not?

My Summary:

  • Sticking to pure foods rather than processed foods will make you feel fuller more quickly, for longer and result in a controlled calorie intake.
  • Always work all of your muscles to avoid losing muscle mass instead of fat when dieting for weight loss. Failure to do so will result in a lighter reading on the scales but no increase in muscle tone or improvement of body shape and firmness. You’ll be “skinny-fat”.
  • If exercising for performance (not weight loss) you should consume carbohydrates before, during and after exercise and a balanced diet of both food types on a day to day basis.
  • A high fat diet is likely to result in more weight loss than a high sugar diet.
  • A combination mix of 50% fat 50% sugar is the nicest but deadliest combination and is likely to result in weight gain if consumed regularly.
  • Sugary diets seemingly aid concentration (if we go by what the TV show found when comparing the TV doctors in an intelligence test)
  • Carbohydrates aid physical performance at higher intensity levels.

If you have the time I would recommend watching the TV show on the BBC iPlayer by following this link: Horizon: Sugar v Fat

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