What is a low-carb diet and is it healthy?

What is a low-carb diet?

A low-carb diet limits your consumption of foods that are high in carbohydrates (carbs). When you digest carbs they turn into glucose, a type of sugar that your body uses for energy. For this reason, a low-carb diet might be used to aid general weight loss, or to help people with diabetes manage their blood sugar levels.

Very low-carb diets include the Atkins diet and the Ketogenic diet, both of which are low-carb and high-fat. The popularity of such diets - helped in part by the celebrities who promote them - has given carbs a bad reputation, but it's important to understand that there are healthy high-carb foods. The fact of the matter is everyone needs carbs in order to perform essential bodily functions and physical activities.

How does a low-carb diet work?

When you consume less energy through food than your body needs, it takes and burns the energy it requires from stores of fat - a process known as ketosis¹. You can trigger fat burning by reducing your intake of carbs and therefore energy. This may result in you losing a significant amount of weight.

Is a low-carb diet good for weight loss?

Registered dietitian Rachel Ball explains when it may - and may not - be appropriate to use this weight loss strategy: "If your goal is to reverse type 2 diabetes, a low-carb diet is one strategy for rapid and significant weight loss. However, this must be with the support of your doctor and dietitian, as your medication doses may need to be changed.

"If you are looking into a low-carb diet for weight loss alone, remember that it is the total calorie intake that is most important, and that there are risks of nutritional deficiency when cutting down a whole food group.

"It's also worth remembering that it is still possible to gain weight when eating low-carb food. Reducing carbohydrates in your diet may lead to you increasing your intake of fat, which is actually higher in calories than carbohydrates, gram for gram.

How many carbs are in a low-carb diet?

A low-carb diet isn't itself a meal plan with a rigid set of rules. This said, the Scientific Advisory Committee on Nutrition (SACN) have produced a report² on lower carbohydrate diets for adults with type 2 diabetes in which they use the following categories:

• Very low-carb/keto diet - 20-50 grams of carbs per day (g/day).

• Low-carb - 50-130 g/day.

• Moderate-carb - 130-230 g/day.

• High-carb - more than 230 g/day.

Ball recommends that people who have type 2 diabetes and are overweight should aim for around 50 - 130g of carbs per day.

"However, many low-carb diet plans fail to define the actual foods you're allowed, and so it is unclear how you can get to these results. Some plans may have a target of total carbs in grams, while others may exclude or limit all grains, potatoes, and rice. This is another reason there is no robust agreement in terms of recommended amounts of carbohydrates."

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Is a low-carb diet healthy?

A healthy, well-balanced diet should include all food groups, and so it's important not to take carb restrictions too far. If you are limiting high-carb foods, make sure that you are making healthy carb food choices. The most common forms are sugars, fibres, and starches. These are further divided into:

• Whole and complex carbs - these are considered healthy because they are minimally processed and are naturally high in fibre as well as other important vitamins and minerals.

• Refined and simple carbs - these have been processed more which removes fibre. Highly processed foods generally lack other nutrients and contain added sugar, which can cause spikes in blood glucose levels. Simple carbs also contain easily digested carbohydrates, making weight gain more likely.

What to eat on a low-carb diet

As far as research goes, the safety and risk factors of following a low-carb diet have been a subject of controversy. In part, this is because these diets are often poorly defined, making it hard to compare studies.

What's more, while there is clear evidence that a low-carb diet can aid weight loss, and help to manage blood glucose levels in diabetes, the long-term health effects of following this diet are unknown³.

Many experts believe that a side effect of a low or very low intake of carbs can result in a nutritionally poor diet, and this may affect a person's overall health⁴.

When is a low-carb diet not always recommended?

• If you are underweight - you should avoid all restrictive diets, including low-carb diets, as this can seriously damage your health, including health problems related to nutritional deficiencies and to your body functions working properly.

• If you have experienced an eating disorder - you should avoid all diets as this could cause a relapse of your condition.

• If you have type 1 diabetes - the most important factor for managing blood glucose for this form of diabetes is the appropriate insulin dose. Low-carb diets could be dangerous if you are taking insulin, so always discuss dietary changes with your diabetes healthcare professionals.

• It's not always appropriate if you have type 2 diabetes - your healthcare professional will advise on the best treatment options for you, including other lifestyle factors and medications.

• It's not always appropriate if you are overweight or obese and at a high risk of developing type 2 diabetes - making certain lifestyle changes while maintaining a diet relatively rich in good carbs is generally considered to be a safe and effective strategy in the prevention of type 2 diabetes⁴. If you have been told you are at risk of type 2 diabetes, always follow the medical advice of your healthcare professional.

Further reading

1. Oh, Gilani, Uppaluri "low carbohydrate diet".

2. The Scientific Advisory Committee on Nutrition (SACN) "Lower carbohydrate diets for adults with type 2 diabetes".

3. Bolla, Caretto, Laurenzi, Scavini, Piemonti "Low carb and ketogenic diets in type 1 and type 2 diabetes".

4. Brouns, "Overweight and diabetes prevention: is a low-carbohydrate-high-fat diet recommendable?".