This week's scientist is Aaron Hengist, a PhD candidate in the Centre for Nutrition, Exercise and Metabolism at the University of Bath. Aaron is investigating how changes to our diet can influence our health and he has provided you a short overview of what we know (and don't know). Enjoy...
Key Question: What do we know about the components of our diet for health?
As we know from Article #2, there are four macronutrients in our diet: carbohydrates, fats, proteins, and alcohol. Each meal we eat has a combination of these, and the body derives energy from this. For many people, carbohydrates make up most of our calories (50 %), with roughly 35 % from fat and 15 % from protein, but this can vary depending on your food choices. There has been a lot of research asking how macronutrients influence health, so here is what we currently know.
The seesaw
One concept which is important to consider is that dietary energy must come from somewhere, so (unless you are in an energy deficit) if you reduce energy from one macronutrient, you have to replace the energy with another macronutrient. For example, if someone reduces their carbohydrates from 50% to 10% of their energy intake, but doesn’t change the number of calories they are eating, the remaining calories must come from either protein, fat, or alcohol.
Carbohydrates
Carbohydrates are chains of sugar. Small chains (with one or two molecules) are called sugars (or monosaccharides/disaccharides), but longer chains are starches (or polysaccharides). Simple sugars are usually absorbed quicker into the circulation than complex carbohydrates. A high blood sugar is harmful for body tissues, so keeping blood sugar at a stable concentration is very important (this will be discussed in future posts). The evidence suggests that eating too many sugars without being sufficiently physically active can lead to a higher overall energy intake, and the development of diseases like type 2 diabetes. Whilst, the UK government suggests people should get less than 5 % of their calories from sugars, many people still get between 10-20 % of their calories from sugars.
More recently, people have asked whether all carbohydrates are harmful for health, rather than just sugars. Whilst they may be absorbed slower, complex carbohydrates can end up as sugars in the circulation. This has led to the popularity of the high-fat or ketogenic diet, which restricts carbohydrates to under 50 grams per day (~ 8 % of daily calories). It is called a ketogenic diet because when the body does not have carbohydrates available, the liver starts to produce something called ketone bodies as an alternative energy source. We don’t yet know exactly how restricting carbohydrates will influence healthy people or people who cannot deal with blood sugar well (e.g. in type 2 diabetes). It is hypothesized that restricting carbohydrates may enable better blood sugar control in people with type 2 diabetes.
Fats
Dietary fats are chains of fatty acids which are linked to something called glycerol. They can come in many combinations, but are most commonly known as saturated or unsaturated. This is based on the chemical composition of the fatty acid chains. The UK government suggests that saturated fats should be replaced by unsaturated fats because there is evidence that reducing the intake of saturated fats reduces the risk of cardiovascular disease, and improves the blood cholesterol profile. Whilst reducing saturated fats may be important for people who are at risk of cardiovascular disease, it is unclear what the effects are on healthy people, especially if they are replacing calories from carbohydrates.
Revisiting that seesaw
So... if you are a healthy person reading this and wondering if it would be better to:
1) restrict carbohydrates and eat more fat; or
2) reduce fat and keep carbohydrates higher
...the answer is... we do not know yet... (yes this is how science works!!)
This is currently an exciting area to study, and is a fast-moving area of scientific research, so stay tuned for updates. In the short-term, a balanced diet consisting of a combination of macronutrients is probably the best option for your health, based on current evidence.
The take home message: If energy intake remains the same, then changing one macronutrient will leads to a change in at least one other macronutrient (like a seesaw). Controlling your sugar and saturated fat intake should have health benefits, but whether a high-carbohydrate or a high-fat diet is best remains to be fully established in science.
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