Spotlight on low-carbohydrate diets

If you're considering cutting back on carbs, make sure you know all the facts first. Nutritionist Kerry Torrens discusses the health benefits of 'good' carbohydrates, and looks at the pros and cons associated with following a restrictive diet.

A piece of bread with a question mark cut out

An introduction to carbohydrates

The type and amount of carbs to include in your diet is a hotly debated topic, with compelling arguments from both sides. But what exactly are carbohydrates?

Most carbs are broken down into a simple sugar, glucose, which is used to fuel our muscles and organs including the brain. Generally speaking, there are three main types of carbohydrates found in our diet and they each have a different effect on our bodies:

What are simple carbohydrates?

Simple carbohydrates are made up of just one or two sugar molecules. They can be divided into ‘naturally occurring’ sugars, found in foods like fruit and milk, and ‘free sugars’ which are either added to foods such as cakes and pastries or found in fruit juice, honey and syrups.

What are complex carbohydrates?

Complex carbohydrates are made up of longer chains of sugar molecules, and are found in starchy foods including jumbo oats, rye bread and brown rice.

What is soluble and insoluble fibre?

Fibre is often forgotten, but nevertheless, it's a very important form of carbohydrate. There are two main types, soluble and insoluble – these are typically found in starchy carbs as well as in whole fruits and veg. Soluble fibre may be found in oats, barley and root vegetables as well as some fruits – studies have shown it may help lower blood pressure and cholesterol. Insoluble fibre is found in wholegrains, vegetable skins, nuts and seeds, and including it in your diet may help reduce the risk of heart disease and stroke. Dietary fibre also helps maintain a healthy environment in the gut.

During digestion, simple carbs break down quickly while complex carbs release their energy more slowly. How the food is processed can also affect how our bodies handle the carbs – refined foods such as white bread will be broken down more quickly, releasing their energy faster. Ideally, the bulk of the carbohydrates in your diet should be complex, unrefined carbs, because they are a rich source of nutrients and dietary fibre. Meanwhile, ‘free’ sugars should be kept to a minimum because they often supply little in the way of nutrition.

Do fruit and vegetables contain carbohydrates?

The natural sugar found in fruit and vegetables is called fructose. While fructose is considered to be a simple sugar, the high fibre content of whole fruit and veg means we digest it more slowly than a glass of juice, which contains the fructose but not much fibre. As a result, eating whole fruit and vegetables containing simple sugars is thought to have a less dramatic effect on blood sugar levels, while also supplying valuable nutrients and fibre.

A colourful selection of fruit and vegetables

What is a low-carb diet?

Currently, there is no official definition of a low-carb diet, although some researchers suggest a diet supplying less than 130g of carbs per day would qualify. There are numerous diets which incorporate some of the principes of low-carb eating, including the Atkins diet and the Dukan diet.

The amount of carbohydrates an individual needs will be unique to them and will depend on their age, sex, gender and activity levels. As a guide, the Reference Intake (RI) for a balanced diet is currently 260g of carbohydrates a day. Those following one of the low-carbohydrate weight loss programmes often aim for less than 50g a day. 

Can low-carb diets promote weight loss?

Cutting carbs may be a useful strategy if weight loss is your goal and your doctor agrees that it will be safe for you. By reducing the carbs you eat you reduce insulin levels and increase a hormone called glucagon which triggers the body to burn fat. However, when you go into this form of fat burning, a process called ketosis occurs and compounds called ketones start to build up in the body. This process can cause side effects including nausea, headaches and fatigue, which can make low-carb diets difficult for some people to stick to.

Much of the weight loss that people experience on a low-carb diet is actually water loss as you deplete your glycogen stores, so some people find that they easily regain the weight when they resume eating carbs. Alternatively, the weight loss may be a result of an overall reduction in calories, rather than as a result of eating less carbohydrate.

Can low-carb diets help to manage diabetes?

There have been a number of news stories suggesting that a low-carb diet may help to manage, or even reverse, type 2 diabetes. Studies do support low-carb diets which are not high in saturated fats as a useful tool for managing type 2 diabetes. Furthermore, research supports a low-carb diet to be as effective as low-fat calorie restriction in terms of weight loss and significantly better for glucose control.

In their position statement on this issue, Diabetes UK cites that there is evidence to suggest low-carb diets may be safe and effective for people with type 2 diabetes. They believe that adopting such a diet may help weight loss and glucose management, and reduce the risk of cardiovascular disease. However, they also say it shouldn't be seen as the diet for everyone and may not be appropriate in the long term. For those with type 1 diabetes there is no strong evidence to say that a low-carb diet is safe or effective. Because of this, Diabetes UK does not recommend low-carb diets to people with type 1 diabetes.

A heart shaped plate on a table

How do low-carb diets affect heart disease?

A widely reported study in 2010 found that women who consumed higher amounts of carbohydrates, most notably simple and refined carbohydrates (those that cause a rapid rise in blood sugar), appeared to have an increased risk of heart disease. These high-GI foods – which included bread, pizza and rice, as well as sugar, honey and jam – appeared to influence inflammation, coagulation and vascular function.

The important factor here is the type of carbs, because other studies demonstrate that consuming complex carbs, including wholegrains and other low-GI foods, may provide significant benefits for the heart.

With specific reference to low-carb diets and heart health, the limited studies available suggest that we need to consider the diet as a whole – in particular the source of fat and protein. This is because when plant sources of fat and protein are chosen in preference to animal sources, low-carb diets may moderately reduce the risk of coronary heart disease.

What research has been done into low-carb diets and long-term health?

There has been plenty of debate over the long-term health implications of following a low carb diet. One 2017 prospective cohort study, covering participants from 18 countries, concluded that high carbohydrate intake was correlated with increased human mortality. A 2018 study concluded that both high- and low-carb diets, as opposed to more balanced diets, were correlated with increased mortality. More specifically, this study supports the findings that low-carb diets which favoured plant-derived protein and fat rather than animal sources, were more likely to be associated with lower mortality. This suggests that the source of protein and fat is an important modifier on long term health and mortality outcomes.

One significant downside to a low carb diet is that it is difficult to achieve guidelines on dietary fibre intake (30g per day). Increasing evidence suggests that the action of beneficial bacteria in our gut when we consume dietary fibre is important for overall health. This is because these bacteria act on the fibre to produce short-chain fatty acids (SCFAs) which prevent the growth of harmful bacteria, keep the gut healthy and may have wider implications for insulin management, weight and immune function.

Nutrition facts sheet with a magnifying glass

Who shouldn't follow a low-carb diet?

Very restrictive diets are not proven to be conductive to long-term health and should be discussed with your GP or health professional before you start. In particular, if you are elderly, under 18 years of age, on medication, have a low body mass index (BMI) or have emotional or psychological issues around food, including any history of eating disorders, you should consult your GP before embarking on any radical change in eating patterns.

Likewise, if you are pregnant, breastfeeding, diabetic or have a condition that requires you to keep a close eye on your blood sugar levels, you should consult your GP or healthcare professional. It should be noted that there have been reports of adverse effects of low-carb diets adopted by children with diabetes including poor growth, a greater risk of cardiovascular disease, and psychological problems. This reinforces the fact that no child should follow a restrictive diet.

If your goal is weight loss and you have a lot of weight to lose, you should seek the advice and guidance of a dietitian to ensure that the diet you follow provides adequate fibre and all the necessary nutrients you need.

Enjoyed this? Now try...

What is the Dukan diet?
What is the Atkins diet?
What is a ketogenic diet?

This page was published on 26 September 2018.

Kerry Torrens is a qualified Nutritionist (MBANT) with a postgraduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Applied Nutrition and Nutritional Therapy (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.

All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other healthcare professional. If you have any concerns about your general health, you should contact your local healthcare provider. See our website terms and conditions for more information.

Comments, questions and tips

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21st Aug, 2017
The problem is that both the food industry and the diet industry are multi billion pound/dollar earning industries. So they want you to eat, get unhealthy and then diet. I saw Lilcassiemoo's comment below. I too started a 21 day diet. Its not high protein as it advocates 20g per portion for a woman for each of the 3 meals which is not too much. Its about learning portions and nutritional value of what you are eating and when. No more eating a 10 oz steak!! I am eating healthier than I have done in years as its forcing me to cook healthy portions of protein and good fats, I have increased my intake of vegetables (which I hate but I need to fill up my calorie quota) and now just eat 3 times a day midday 4pm and 8pm. I am managing to attend the gym, no dizziness, no trouble with my 'movements' either. Don't get me wrong - personally I would love to be sitting on the sofa with a whole Sourdough loaf and a tub of butter, or 10 bags of chocolate buttons. But this diet is teaching me all in moderation. So if I have been good for the day I can allow myself 3 digestive biscuits (approx. 30g carbs) as a treat. Rest of my carbs are from vegetables. I lost 8 pounds on my first week, and 6 on my second just into my third week and am feeling fantastic. I hate vegetables but if eating high vegetable, weighed out good proteins and good fats is doing this to me then bring it on. If my weight goes down so does my risk of Type !! diabetes, and my high blood pressure and all the other things that task us as we get older. Bread love it, Potatoes love them, biscuits - 3 weeks ago I would have eaten a packet at a sitting because I have a sweet tooth. Now I avoid it all, no snacking either. You have to just find what works for you and keep advised by your own doctor if you have questions I think . Good luck everyone on whatever you are eating - enjoy ;o)
21st Jun, 2017
Mmm A very simplistic article for a very complex topic Stay away from it BBC or do it properly Please do not use nutritional therapists from BANT or links to complementary medicine organizations Rather, use proper nhs dietitians Readers beware of the above article it's Simplistic
7th Mar, 2017
Thank you to all who commented on the benefits of Low Carb Diets! I'm just beginning with it, sticking to under 50 g of carbs from veggies, and I'd say I feel quite alright. I certainly consume a lot of fiber, my gym performance is the same as before, and I'm not lightheaded in the least. I guess I'm finally eating what my doctor recommended for anemia some years ago. I'm surprised that the author of this article presents the Low Carb Diet in such a negative light. Most of the Low Carb misconceptions listed on other sites are quoted here as facts. Also, the new research that shows the importance of fats has been ignored. Yes, whole milk (plain) yogurt is way healthier that the low fat alternative! Some of the comments seem to go overboard, thought. Carbs are not toxic, as long as you get them from veggies, fruit, and whole grains, and consume in moderation. Let's not get too dogmatic while defending the Low Carb Diets.
6th Mar, 2017
Yes, well, I've just been through this myself for the first time in 65 years, and I can tell you, carbs are not the problem. Parasites are the problem. Mostly everyone is infected, the soil is infected and these little chums go through the cycle from animals to humans where they may be unseen and undiagnosed for years, until you start to have digestive problems because the worm has used up all your enzymes, or joint problems or bone pain or sleep disturbance or any of the dozen disparate symptoms that they produce, and the medical community, in it's drive to create medical robots, has deliberately ignored. Big Pharma, Big Medicine and Big government have been fooling you. What is needed is not more diets, certainly not more antibiotics, but the declaration of a public health emergency the likes of which we have never seen before. More than 4 Billion people world wide are infected, yet NO ONE, not your doctor, not the government and certainly not your friends talk about it. It does no good to treat Joe and Jane, if 50 million people on the continent or more, can come and go and leave little packages for other to become infected with. I found a tapeworm in me that had been there for 60 years. It wasn't until I realized that my suspicions about picking it up in a near drowning incident near a slaughterhouse were confirmed, that I began to realize what a catastrophe parasites of all types are to people. In deed, it has only been since the early part of this century that they had even been able to culture properly for these things.
6th Mar, 2017
''such strict dietary approaches are not conducive to long-term health '' Prove it. The article boasts 'the facts on low carbs' and then expresses mostly opinion. Eating low carb has changed my life, I have never been so well, ate in so much variety, far from finding it restrictive I have found it freeing.
17th Aug, 2016
I am so chuffed to be reading all these fabulous helpful comments. Myself and my daughter have struggled for years doing many different diet's where you eat loads ones where you count points and the weight losses have been so slow or non existent soul destroying. My daughter found a 21 days paleo diet which I found a bit extreme so after adapting a little we are basically on a very low carb high protein and fat diet. Wow it's working 12.5lb off in 8 days. We eat from midday to 6-7pm and fast for the rest if the time, it's all back to basics of meat, veg, salad, limited fruit, nuts, yogurt, coconut's amazing. We sleep really well. No toilet trouble. No bad breathe. Loving it and can only recommend highly that cutting out crap processed junk and carbs works. The science behind it is amazing.
25th Jun, 2016
I have been on a low carb diet for years and this "nutritionist" has her facts all screwed up, particularly where "safety" is concerned. First, nutritionists like her have been pushing the wrong dietary advice on us for the last 40 years that have gotten us to the point of the low carb diet, or as I'd like to say, back to where humans use to be. She says bad breath is a side effect. I've been low carb for several years. The only time I have bad breath is my food is flavored with garlic or some other spice. Mouth wash takes care of that. There is no evidence that supports the theory that a diet high in protein causes kidney damage, unless the kidneys have had troubles functioning prior to the low carb diet. Fiber...there is evidence to suggest that fiber can be rather harmful and that it is not even needed in the first place. I can attest to the fact that I eat little fiber, however, I have no issues with bowel movements. Want issues with bowel movements? Consume too much fiber then head to the doctor to look at that bowel obstruction. Dizziness, insomnia, nausea --- think there aren't other things in your life that don't cause those conditions? Brain fog is temporary until the body adjusts to using ketones for energy and the brain can use those just as nicely as glucose. However, a low carb diet that is too low may cause gluconeogenesis, which is when the body converts protein to glucose --- only after the body breaks down protein for its other uses. I am not a nutritionist but know these things. Yet it doesn't surprise me that this nutritionist does not. Most don't.
13th Jun, 2016
After years of being a borderline diabetic my yearly hba1c test showed +ve and combined with cholesterol of 7 a change was due.. With advice from a book' how to reverse your diabetes' I changed to a low carb diet. My weight has gone from 123kg to 99kg and my cholesterol from 7 to 4.3. 'Nice 'guidelines say low fat high carb diets are best but people are now smelling the coffee and realising that all the latest healthy manufactured foods and advice don't work. At a recent visit to a diabetic nutritionist I was told that nice guidelines dictated the advice that she could officially give me and was advised to eat more carbs and eat less fat ! Luckily my doctor is switched on and is quite happy with my progress and choices.
25th Apr, 2016
I've been on a low carb, high fat diet for two years and eat plenty of fibre ( from green veggies). Constipation has never been an issue! Broccoli, kale, spinach and the like give me loads of fibre, as well as tons of vitamins and minerals. Think you don't like greens much? Drown them in butter and I promise you they'll taste great! Don't listen to the "glucose is the best fuel" guff! My brain is working perfectly well, thank you. No dizziness, no cloudy thinking, no headaches and much better sleep than when I was on the so- called ' balanced diet'. Oh and by the way, I've lost 5 inches off my waistline without starving myself. LCHF is LOW carb, not NO carb ( which is probably impossible to achieve, even if you wanted to do it). Moderation in all things? No thanks! Ditch the sugar, drop the processed carbs massively and replace them with LOTS of healthy fats, such as avocado, olives, full fat yoghurt, cheeses and fatty meats and offal. It may not work for everyone, but many could transform their health by not listening to out dated, old school nutritionists.
ladoll0606's picture
2nd Jan, 2016
Hallelujah for LCHF! It's changed my world! Some real bad research re side affects!! Been LCHF for a year now and have NEVER been constipated - what BS (pun intended).


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