Sugar vs Fat: Which is Worse?

Sugar or fat, which is worse? That’s the question in a recent BBC documentary..

It’s an interesting setup. Two identical twin brothers – both of them doctors – go on a diet for a month. One on an extreme low fat diet, one on an extreme low carb diet (not even vegetables are allowed!).

One twin gave up sugar, the other gave up fat. The findings were more or less what could be expected:


Even though both brothers were at a fairly decent weight to start with, the low-carb brother lost the most weight: 4 kg (9 pounds) vs only 1 kg (2 pounds) for the low-fat brother.

The loss of fat was 1,5 kg on low-carb (a good result in a month) and 0,5 kg on low-fat. Most of the rest was probably fluid. On a very strict low-carb diet you quickly lose a kilo or two of glycogen and water weight.

How much – if any – muscle mass the participants lost is impossible to know as the  test only measures fat mass vs. non-fat mass (including water).

Weight loss should never be the only, or even the most important goal – achieving vibrant health should be the priority; then optimum weight will be the result.

Brain function

For testing the brain function of the brothers the producers chose to make them do stock trading with fake money.

This test is rather dubious, but the low-fat brother wins.

More interesting and relevant is that the low-carb brother complained of feeling “thick-headed”.  Going on an extreme low-carb diet – without even vegetables – can absolutely result in problems concentrating, etc.


For testing their exercise capacity the brothers did “long sessions of uphill cycling”. The low-carb brother predictably loses badly.


The documentary concludes that it’s not about fat or sugar, it’s about avoiding processed food with both fat and sugar in it. This is an excellent start, but not enough.

It’s even more important to focus on what we DO eat. As Dr. David Katz says: “Mostly plant-based diets add years to your life and life to your years.” … and Michael Pollen: “Eat food, not too much, mostly plants.”

So let’s eat lots of fruits, veggies, berries … ie. plants; and focus less on what we should not eat … sugar, fat, etc. That’s a ‘glass is half full’ approach, rather than ‘half empty’. In fact, “the glass is half full and the other half was delicious!” should be our motto!

We have a proven program for achieving vibrant health – just in case you are interested: Transform2014.