The Case for Carbs

Part two of our macronutrient blog series will be a deep dive into carbohydrates: what they are, their role in the body, sources in the diet and how they can play a role in health and fitness. 

Carbohydrates: Fuelling the Body with Smart Energy

Carbohydrates are often at the heart of nutrition discussions, and for good reason. As one of the three essential macronutrients, alongside protein and fat, carbohydrates play a central role in providing energy to the body. Despite often being misunderstood or unfairly criticised in some dietary trends, carbohydrates are vital for optimal health, especially when consumed in their most nutritious forms (1)

In this article, we’ll break down the science of carbohydrates, their role in human physiology, and why choosing high-quality, fibre-rich sources can benefit your health, energy levels, and performance.

What Are Carbohydrates?

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. They are found in a wide variety of foods, particularly those containing starches and sugars. When we consume carbohydrate-containing foods, the body breaks them down into glucose; a simple sugar that serves as the body’s primary and most efficient source of energy. (2)(4)

There are two main types of carbohydrates, classified by their chemical structure and digestion rate: (3)

• Simple Carbohydrates
  These consist of one or two sugar molecules and are quickly digested, leading to rapid spikes in blood glucose. Examples include glucose, fructose (found in fruit), and sucrose (table sugar). Common sources include sweets, sugary drinks, and processed snacks.
• Complex Carbohydrates
  Composed of longer chains of sugar molecules, complex carbs take longer to break down, providing a more sustained release of energy. They are typically found in wholegrains, legumes, starchy vegetables, and minimally processed foods, and are also rich in essential nutrients like fibre, B vitamins, and minerals.

How Carbohydrates Work in the Body

The digestion of carbohydrates begins in the mouth, where enzymes in saliva start breaking down starches. This process continues in the small intestine, where complex carbohydrates are further broken down into glucose. Glucose is then absorbed into the bloodstream and: (3)

• Used immediately for energy
• Stored as glycogen in the liver and muscles for later use
• Converted to fat if consumed in excess and energy needs are already met

This process ensures a steady fuel supply for everything from everyday tasks to intense physical activity. (5)

Why Are Carbohydrates Important?

Carbohydrates serve multiple essential functions: (1) (4)

• Primary Energy Source: Especially for the brain, nervous system, and during physical activity.
• Metabolic Health: Critical for efficient energy metabolism, particularly when consumed as part of a balanced diet.
• Exercise Performance: During both aerobic and anaerobic activity, glucose and glycogen are the body’s preferred fuel sources, especially at higher intensities.
• Nutrient Delivery: Whole carbohydrate sources provide fibre, vitamins (especially B-complex), and minerals (like iron, magnesium, and zinc).

Inadequate carbohydrate intake can lead to fatigue, poor concentration, and decreased physical performance – and not necessarily just performance in exercise!

The Importance of Fibre

One of the key benefits of complex carbohydrates is their fibre content. Though fibre is a type of carbohydrate, the body cannot digest it; but that’s exactly what makes it valuable. (5)

Types of Fibre:

• Soluble Fibre dissolves in water and can help lower blood cholesterol and glucose levels. Found in oats, beans, apples, and citrus fruits.
• Insoluble Fibre adds bulk to the stool and promotes healthy digestion. Found in wholegrains, nuts, and many vegetables.

Fibre has many health benefits including support heart health, reduces risk of type 2 diabetes, aids digestive health and lowers inflammation. For more information on Fibre, look out for our upcoming Fibre blog!

Sources of Carbohydrates

Carbohydrates are found in both healthy and less healthy foods. The quality of the carbohydrate source has a significant impact on health outcomes. (6)

Nutritious (Complex) Carbohydrate Sources:

• Wholegrain bread, pasta, and rice
• Oats and other wholegrain cereals
• Legumes (lentils, beans, chickpeas)
• Fruits and vegetables
• Potatoes and sweet potatoes

These foods offer energy along with important nutrients and fibre.

Less Nutritious (Simple) Carbohydrate Sources:

• Sugary drinks, sweets, and chocolate
• Cakes, biscuits, and pastries
• White bread, white rice, and refined cereals
• Crisps and other processed snacks

While these may provide rapid energy, they lack fibre and essential nutrients. Frequent consumption can contribute to blood sugar instability and long-term health risks. However, in some contexts, such as endurance sports, these fast-acting carbohydrates can be beneficial for maintaining energy levels.

Carbohydrates and Exercise: Strategic Fuelling

For physically active individuals, especially those engaging in endurance activities (e.g., running, cycling, swimming), carbohydrates are essential: (7)

After Exercise: Replenish glycogen stores with a combination of carbohydrates and protein to support muscle recovery and repair.

Before Exercise: Consume slow-releasing carbs (e.g., oats, wholegrain toast, sweet potatoes) 1.5–2 hours beforehand to build glycogen stores.

During Exercise: Rapidly absorbed carbs (like sports drinks, bananas, or gels) can help maintain energy levels during prolonged activity.

Friend or Foe?

Carbohydrates are a cornerstone of a healthy, balanced diet. When chosen wisely, focusing on whole, minimally processed sources, they provide not only energy but also the nutrients and fibre essential for long-term health and wellbeing.

Rather than eliminating carbs, focus on quality over quantity: build your plate with wholegrains, legumes, vegetables, fruits, and starchy root vegetables. Your body and your energy levels will thank you.

Top Tips

1. Focus on quality over quantity
2. Know the difference between simple and complex carbohydrates
3. Fuel your performance properly, before, during and after… particularly for endurance sports
4. Focus on fibre, as your body cannot produce this on its own
5. Carbohydrates are not the enemy, they are an essential part of a healthy, balanced diet!

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References

1. National Library of Medicine, 2023, Physiology Carbohydrates. Available via: Physiology, Carbohydrates – StatPearls – NCBI Bookshelf
2. British Nutrition Foundation, 2023, Starchy Foods. Available via: Starchy Foods (Carbohydrates) – Nutritional Information
3. Cold Spring Harbor Perspectives in Biology, 2021, Carbohydrate Metabolism. Available via: Carbohydrate Metabolism
4. National Health Service, 2022. Starchy Foods and Carbohydrates . Available at: https://www.nhs.uk/live-well/eat-well/food-types/starchy-foods-and-carbohydrates/
5. Nature Reviews Gastroenterology & Hepatology, 2020, Dietary Fibre in Gastrointestinal Health and Disease. Available via: Dietary fibre in gastrointestinal health and disease | Nature Reviews Gastroenterology & Hepatology
6. Science Direct, 2021, Simple Versus Complex Carbohydrate and Health: A Frequently Neglected Problem. Available via: Simple versus complex carbohydrates and health: A frequently neglected problem – ScienceDirect
7. Springer Nature Link, 2022, The Ergogenic Effects of Acute Carbohydrate Feeding on Resistance Exercise Performance: A Systematic Review and Meta-analysis. Available via: The Ergogenic Effects of Acute Carbohydrate Feeding on Resistance Exercise Performance: A Systematic Review and Meta-analysis | Sports Medicine

Author: Jessica Eardley-Thompson, ANutr Nutritionist
Editor: Lucy Clarkson, SENr Nutritionist & Grace Williams, Head of Nutrition and Operations