Carbohydrates

by our Sports Nutritionist Kate Shilland

Nutrition advice is ripe with anecdotal evidence and unfounded claims about food. Despite the current surplus of new information, the way our bodies use food for fuel hasn’t ever changed. We’re running a series of back to basics, evidence-based fact sheets to provide you with a go-to source of reliable information.

First up; carbohydrate.
What are carbohydrates, other than a hotly debated topic, heading the charts of foods we love to hate? The idea that ‘carbs are bad’ has left us confused about carbohydrates and their importance for our health.

So, keeping it simple, here’s our carbohydrate fact file.

WHAT ARE CARBOHYDRATES?
Carbohydrates are one of the three macronutrients in our diet. They are subdivided into 3 categories: sugar (simple carbs), starch and fibre (complex carbs), this is based upon the structure of their saccharide (sugar) units.

Understanding type, quality and quantity of carbs is key for health and performance.

Sugar: Sweet tasting foods containing single sugar compounds or short chains of single sugar compounds – in foods such as fruit, table sugar. These are also the sugars added to food or drinks, including sugars in biscuits, yoghurts, cereals and fizzy drinks. They are quickly digested and cause a sharp rise and subsequent steep fall in blood sugar levels.
Starch: Starch is found in plant-based foods such as bread, rice, potatoes and pasta that contain long chains of sugar compounds. These provide a slower and steadier release of energy than simple sugars.

Dietary fibre: Fibre rich foods contain long chains of sugars that the body can’t break down so they pass through the gut undigested. They include wholegrains, beans, pulses, nuts, seeds and root vegetables and they release sugar into the bloodstream more slowly than sweeter tasting foods. Fibre has been shown to have multiple health benefits, from reducing risk of heart disease, strokes and colorectal cancer but is something that, as a nation, we’re not that great at consuming enough of.

Why do we need carbs?
Carbohydrates are your body’s preferred energy source. They are the primary fuel for the brain, central nervous system and exercising muscles. Despite accounting for only 2% of our body weight, the brain uses roughly 20% of our daily energy expenditure, in the form of glucose, so it’s pretty important not to cut out.

Whether carbs come in the form of a simple sugar or starch, once digested, they are all broken down into glucose and absorbed into the bloodstream to act as a fuel source for every cell in the body. This process is quicker for simple carbs.
Unlike fat, the body’s storage capacity for carbohydrates is limited – approximately 80-110g stored in the liver and 300-600g stored in muscles, depending upon your size. Stores are depleted by exercise and daily activity, so it is important to top them up through food. When blood sugar levels drop, your physical and mental performance decreases. We’re all familiar with that fatigued, irritable and foggy headed feeling.

How much?
Data from the National Diet and Nutrition Survey, which looks at food consumption in the UK, shows we should focus on swapping simple and processed carbohydrates for nutrient-packed, fibre-rich to help you keep healthy and sustain energy levels for longer. Whilst your carbohydrate needs vary from day to day, depending on your activity, current guidelines recommend approximately one-third of your diet to be starchy foods, such as potatoes, wholegrain bread and pasta and another third fruit and vegetables.

Like anything; if you eat more carbohydrates than your body can store as glycogen, some of this surplus will be converted to fat. But, this only happens when your overall daily calorie intake exceeds your daily expenditure. Carbs don’t make you gain weight, positive energy balance makes you gain weight, regardless of the calorie source.

The take home message:
Carbs are an essential fuel for the brain, central nervous system and muscles. Rather than touting the good, the bad and the ugly, the key is to turn the focus to the right type in the right quantity for your specific requirements. They are an essential macronutrient required for optimal health and performance in varying quantities depending upon your individual requirements. It doesn’t have to be complex. Unless it’s a carb of course.

References

1. Hardy, K (2015), The Importance of Dietary Carbohydrate In Human Evolution.’ The Quarterly review of biology, 90 (3), pp. 251-68
2. Great Britain. Scientific Advisory Committee on Nutrition and Stationary Office (Great Britain) Carbohydrates and Health.
3. NDNS: results form years 7&8 (combined) – GOV.UK
4. Magistretti, PJ & Allaman I; A Cellular Perspective on brain energy metabolism & functional imaging. Neuron Review, May 2015
5. Te Morenga L, Dietary sugars and body weight: systematic review and meta-analyses of randomised controlled trials and cohort studies. BMJ. 2013; 346: e7492
6. Reynolds A, et al, Carbohydrate quality and human health: a series of systematic reviews and meta analyses. Lancet. 2019; (published online Jan 10.)
7. Kreitzman, S.N (1992) ‘Glycogen storage: illusions of easy weight loss, excessive weight regain and distortions in estimates of body composition. ’The American Journal of Clinical Nutrition, 56(1), p. 292S-293S