Are Carbohydrates Fattening?

Carbohydrates have received a battering in the media over the past few years.

As a result, many people consider carbs to be “unhealthy” and “fattening”.

Should we be fearful of carbs? Or do they have a role in the context of a balanced diet? This article provides an evidence-based overview.

What are carbohydrates?

Carbohydrates are one of three main macronutrients in the diet – carbohydrates, protein and fat.

Carbohydrates are the main source of energy for the human body, and are necessary for a healthy and balanced diet. Most carbohydrates are digested in the body into glucose (sugar) molecules – the body’s preferred source of energy.

There are three main types of carbohydrates:

  • Sugars – single or short chains of sugar molecules

  • Starches – long chains of sugar molecules

  • Fibre – a type of indigestible carbohydrate found in the cell walls of plant foods

Sugars can be found naturally in milk, fruits, and vegetables. They’re also added to food or drinks such as sweets, flavoured yoghurts, breakfast cereals and fizzy drinks; these are called free sugars. Free sugars are also found in honey, syrups, nectars, unsweetened fruit juices, vegetable juices, and smoothies.

Starchy foods include bread, rice, pasta and potatoes. Opt for whole grain starchy foods such as whole grain bread, brown rice and wholemeal pasta, as these release their energy (sugar) more slowly than their refined counterparts (i.e. white bread).

Finally, fibre refers to the portion of plant-foods which cannot be digested in the small intestine. Instead, it’s digested in the large intestine by healthy gut bacteria, which has beneficial effects for our health.

High-fibre foods include:

  • Fruits and vegetables (with skin on)

  • Pulses

  • Legumes

  • Whole grain cereals

  • Nuts and seeds

How much carbohydrate do we need?

For most healthy individuals, around half of your daily calorie intake should come from carbohydrates (1).

Adults should try to consume at least 30g of fibre each day. However, average intakes are much lower than this, with most people consuming just over half the recommended amount per day (2).

Free sugars should make up no more than 5% of our total daily calorie intake (about 100 calories per day for an average female). Again, most UK adults are eating nearly double this recommended amount (2).

Are carbohydrates bad?

Carbohydrates are a diverse food group and different types of carbs have different health benefits.

Classifying a food group as ‘good’ or ‘bad’ is unhelpful. All foods have a place in a healthy, balanced diet, so it’s better to focus on including the right types of carbohydrates in your diet rather than cutting things out all together.

Eating too many free sugars is associated with weight gain and poor dental health. (2). You can cut down on your intake of free sugars by:

  • Checking nutrition labels for foods with no added sugars

  • Adding fruit to meals for sweetness, rather than jams, syrups, and spreads

  • Limiting fruit juices and smoothies to no more than 150ml a day

  • Not adding sugars to drinks such as tea and coffee

Fibre is crucial for good digestive health, as well as helping to reduce the risk of many chronic health conditions such as type 2 diabetes, cardiovascular disease, and colorectal cancer. (3, 4, 5, 6).

You can increase your fibre intake by:

  • Choosing wholegrain foods (such as bread, cereals, and pasta)

  • Eating whole fruits rather than juice

  • Increasing your consumption of beans, legumes, and vegetables

  • Having fruit, nuts and seeds for snacks

Will carbohydrates make me fat?

Contrary to popular belief, carbohydrates contain the least number of calories per gram compared with other macronutrients.

  • Carbohydrates – 4kcal/gram

  • Protein – 3.75kcal/gram

  • Fat – 9kcal/gram

Interestingly, a high fibre intake is associated with lower body weight and body fat (7). Fibre is thought to affect body weight in several ways, including:

  • Making us feel fuller (8)

  • Slowing down the rate at which our stomachs empty (9)

  • Keeping our gut bacteria healthy (10)

Some research has also shown that increasing fibre intake is associated with a reduction in calorie intake, even when calorie intake isn’t restricted (11) High fibre foods also tend to be lower in fat and calories.

It’s not the carbohydrates themselves that are fattening; it’s what we put on them that matters. Any food can cause weight gain if you regularly eat more than your body needs. Being mindful of portion sizes is important, regardless of the type of food being eaten.

Are low-carbohydrate diets good?

Low carbohydrate diets may lead to a small but significantly greater weight loss (about 2kg) compared with traditional low fat diets (12, 13).

Low carb diets have also been shown to be effective in improving blood sugar control in diabetics as well as having favourable effects on cardiovascular risk factors (14, 15).

It would appear that consuming a low carbohydrate diet with less than a quarter of your total energy from carbohydrate foods (approximately 130g of carbohydrate per day) has the most beneficial effects on cardiovascular blood markers.

Very low carb diets (i.e. the ketogenic diet) contain around 20-50g carbohydrate per day and can result in impressive weight loss, but we don’t know much about long-term effects on our health.

Cutting carbohydrates from your diet is difficult to stick to. Plus you’re likely to miss out on the health benefits associated with whole grains and fibre. It requires careful planning and ideally supervision from a Registered Dietitian to ensure sufficient nutritional adequacy.

There remains strong evidence to support the health benefits of a balanced and unprocessed diet which is rich in wholegrains carbohydrates, pulses and legumes. So there’s no need to ditch carbohydrates after all!