Sugar vs Fat: A revelation or what we already knew?

Emma Brown - Nutritionist | 01 Feb, 2014

It's been a long month full of news articles and TV programmes about health, dieting and nutrition, so I was pleasantly surprised to watch Horizon this week on BBC2, and to find a relatively balanced report about the sugar vs fat debate.

The plethora of celebrity diets out there has meant a focus on single nutrients, and how cutting down (or even cutting out) in your diet can support weight loss and improve health. Whether it's the low carb Atkins, Dukan or South Beach, or the high protein/ high fat Paleo, diets taking out food groups or nutrients have become ever popular.

The premise of the programme was to investigate whether having a diet low in sugar or a diet low in fat actually made any difference. Identical twin doctors took on the challenge, and followed extreme diets for 1 month – being identical twins meant that genetics were the same, and therefore this element of difference could be taken out of the equation.

Before setting off on the diets, the doctors were put through a series of gruelling tests measuring everything from weight and BMI, to cholesterol and insulin levels right through to fitness capacity.

What did the diets look like?

One twin followed a very low carbohydrate diet (almost carb free) which consisted of lots of meat and dairy but no bread, pasta, fruit or veg. The other twin followed a very low fat diet – rich in carbohydrates both complex and simple, so plenty of breads, pasta, grains, cereals, fruit and veg, but also cakes, biscuits, sweets and fizzy drinks.

Sticking to the diet was tough for both – the low carb diet was hard to stomach after a while, and the lack of fruit, veg and fibre meant digestive problems like constipation, and an inability to concentrate or perform in tasks (due to a lack of glucose getting to the brain). There was also the issue of exercise – very tough for anyone not having carbs in their diet. The low fat diet meant no meat and little protein, and a realisation that it's often the fat in food that makes it taste good and feel appetising.

The results

Oils Sugar Fat

What surprised me the most was the results on insulin and blood glucose control. There's a common belief that having too much sugar in the diet predisposes to developing Diabetes despite a lack of evidence to actually support this.

Here the twin following the high sugar/ high carb diet appeared to compensate for the extra sugar in the system by raising insulin levels, and basically 'dealing' with the extra sugar. In contrast, the high fat twin developed a 'resistance' to insulin because of the amount of fat in his system. Shockingly he was told that he was just one step away from developing Diabetes. So this questioned the whole debate about whether sugar does play a role in diabetes risk, or is it actually fat?

The other scary result was around muscle mass – the high fat diet resulted in a larger loss of muscle mass overall, and this was probably because the body had had to use protein (from the muscles) to make essential glucose for the brain. Without any glucose coming from the diet, the body needs to find it from somewhere, especially during exercise, and this will be at the expense of muscles. Muscle is one of our most important metabolic tissues (this is where we burn calories) so losing muscle mass isn't a positive result.

So what does it all mean?

Obviously this was a study of just two people but I think it gave us a fascinating insight into what extreme diets might be doing to our bodies. The doctors, and nutritional experts on the programme, both highlighted that cutting out one nutrient doesn't actually seem to make any positive impact on weight or health, but that it's the combination of the two, fat and sugar that has the biggest effect.

Fat with sugar makes food taste good, and we have an innate preference for food with a 50:50 ratio of the two. So it's not a case of saying 'I'll cut out carbs and be healthier', or 'I'll go fat free and be healthier' – the evidence is clear that body weight is a much greater indicator of health risk, than any one nutrient.

Being a healthy body weight cuts the risk of developing diabetes, heart disease, some cancers and many other conditions, so it's about being sensible about the amount of food we eat, and making sure that we're not taking on extra calories that we don't need.

Professor Susan Jebb, an eminent nutritionist, summed it up by saying 'it's a wonder that anyone in the UK is actually slim' because we have unlimited access to so much, and such good tasting food. It's true – we are surrounded by temptation, but that doesn't mean we have to give into it!

The Nutracheck Way

So we're back to our mantra – it's about balance. Eat a healthy, balanced diet including all the food groups, keep an eye on portion sizes and make healthier choices (less processed foods) where you can.

We like to keep things simple.

If you manage to eat regular meals, choose more complex carbs, have 5 portions of fruit and veg, choose lean meats or veggie options, choose lower fat dairy foods and keep treats as treats, then there's no reason why you shouldn't lose weight, and reduce your health risk factors at the same time.

Remember every nutrient is important. Eating a variety of different foods will mean you get a wide range of nutrients – each has a role to play.

Nutritionist Emma Brown (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.