Spotlight on... low-carbohydrate diets

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

Spotlight on... low-carbohydrate diets

An introduction to carbohydrates

Dietary carbohydrates play a central role in nutrition because they are the body’s primary source of energy and are important for the proper function of everything from muscle contractions to brain activity. Carbohydrates are classified into two basic groups: simple and complex:

Simple carbohydrates
As their name suggests simple carbs are just that - typically one-sugar molecules (mono-saccharides) or two-sugar molecules (di-saccharides). This category includes refined carbohydrates, which are rapidly digested and release sugar quickly into the bloodstream. They are good when a quick, readily availble source of energy is required, for instance before or during exercise. However, if eaten too regularly and in large amounts they can leave you feeling unsatisfied and prone to energy highs and lows. Examples include white bread, honey, pastries and biscuits.

Complex carbohydrates
These starchy carbs are made up of many simple sugars joined together by bonds - the more bonds, the more complex and the longer the carbs take to break down. Eating complex carbohydrates can reduce the chances of feeling fatigued or hungry between meals.  The best examples are those that have undergone the least processing – such wholegrains include jumbo oats, brown rice, spelt, rye and barley.

Ideally complex carbohydrates should make up the bulk of your carbohydrate consumption, as they are the best source of nutrients and fibre. 


ResearchHeart disease

Some research suggests that excessive consumption of carbohydrates – specifically, simple carbohydrates - can be harmful to blood sugar control, especially if you are insulin resistant, experience reactive hypoglycaemia or are diabetic. Carbohydrate excess, especially consuming too many refined carbohydrates, is sometimes associated with weight gain and increased risk of heart disease and some forms of cancer.


Fruit & vegetables

The natural sugar found in fruit and vegetables is called fructose. While fructose is considered to be a simple sugar, the high fibre content means the body digests whole fruit and veg more slowly than say a biscuit that contains no fibre but high amounts of white sugar. As a result, eating high fibre foods containing simple sugars is thought to have less of a dramatic effect on blood sugar levels.


balanced dietLow-carb diets and weight loss

The Reference Intake (RI)  for a balanced diet is currently 260g of carbohydrates a day. People following a low-carbohydrate diet often try to stick to less than 50g a day.

Ketosis is often a by-product of a low-carbohydrate diet. Ketones are produced when the body’s glycogen stores have been used up and protein and fat become the primary source of fuel.

Because food choices are limited, low-carbohydrate diets tend to be low in calories yet high in protein and fat. Fruit, bread, grains and starchy vegetables are often limited. The proportion of protein and fat is increased to contribute towards the calories that formerly came from carbohydrate sources. 

The Atkins diet and The Dukan diet are well-known ‘classic’ low-carbohydrate programmes, while other plans focus sometimes on the glycaemic index of foods. The glycaemic index (GI) is a rating system for foods based on the extent to which they raise blood sugar levels in the hours after they are eaten. The reference point is pure glucose which is scored at 100. The higher a food scores on the GI scale, the more rapidly the carbohydrate (sugar) is released into the bloodstream. 


Low-carbohydrate diets, if followed over a consistent period of time, present a number of health concerns. Such a diet is likely to be low in fibre which may lead to digestive issues including constipation. The lack of carbohydrate in the diet means the body doesn’t have a ready supply of glucose, the brain’s primary source of fuel – this may lead to dizziness and headaches as well poor concentration. Other side effects include halitosis, insomnia and nausea. In addition to this the likely increase in the proportion of protein in the diet places an additional load on the kidneys and may lead to problems with bone-health.

While the exclusion of all carbohydrates often means less refined sugar in the diet which can only be a positive benefit to health, such strict dietary approaches are not conducive to long-term health and should be discussed with a GP or qualified health professional before you start.


More information and recipeslow-carb recipes

Read our nutritional therapists view on two low-carbohydrate diets:
What is the Atkins diet?
What is the Dukan diet?

If you’ve read all the factsand want to include some low-carb options into your balanced diet, our recipe collection has some delicious suggestions, all containing under 10g of carbohydrates per serving:
Low-carbohydrate recipes


Jo Lewin holds a degree in nutritional therapy and works as a community health nutritionist and private consultant. She is an accredited member of BANT, covered by the association's code of ethics and practice.


This article was last reviewed on 27 May 2016 by nutritional therapist Kerry Torrens.

A registered Nutritional Therapist, Kerry Torrens is a contributing author to a number of nutritional and cookery publications including BBC Good Food magazine. Kerry is a member of the The Royal Society of Medicine, Complementary and Natural Healthcare Council (CNHC), British Association for Applied Nutrition and Nutritional Therapy (BANT).

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 health care professional. If you have any concerns about your general health, you should contact  your local health care provider. See our website terms and conditions for more information.

Comments, questions and tips

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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).
20th Apr, 2015
This dietry thinking is becoming outmoded as more specialists realise that carbohydrates are toxic. The body needs fat, yes fat, and lots of it to function effectively. The explosion in obesity and diabetes has been exacerbated by the focus on the outdated and inaccurate low-fat, high fibre diet. You reduce blood sugar by eating high fat protein and little or no carbs. You lose weight by doing the same. Fatty protein has no effect on Cholesterol and can be beneficial by raising HDL. All that carbohydrates do is pump excessive sugar into the blood stream causing the Pancreas to work overtime producing the fat hormone Insulin. This mean all the excessive sugar is converted to fat by insulin - carbohydrates make you fat, sluggish, fatigued and hungry. so you eat more carbs etc...eventually the pancreas can't cope and you become insulin resistant and diabetic; like me! The truth is out there you just need to look and read. Oh, by the way, if you're worried about constipation don't be - high fibre diets don't help it but low fibre diets do.
24th Jun, 2015
Symbiotic has it right. This is old-fashioned dietary advice. We don't actually needs carbs in our diet at all. We can live without them. The research shows that while there are some side effects initially in low or no carb diets, these are short term. Cutting carbs and increasing fat and protein is better for risk of heart disease, cancer and atherosclerosis. There is no science supporting the notion that sat fat causes these things but some research showing the dangers of high GI foods.
6th Nov, 2014
I've been on a low-carb diet for most of my adult life and this is the only diet that has ever worked for me. I guess it's different for different people, but I always gain weight when I'n not on a low-carb diet, so I've made a conscious effort to adjust my lifestyle so I can minimize carbs, and improve my health in the process. You can check out my site if you are interested in a low-carb lifestyle.
7th Oct, 2014
I tried a low carb diet a couple of times but just couldn’t sustain it (hey I love pasta and bread :-)). Once I found a diet that I could stick to and was still able to eat foods I liked in moderation, I finally lost the baby weight. There's a good overview of the program I followed at for anyone else who struggles to reduce carbs
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8th Jan, 2016
A low carb vegetarian diet is helpful in weight loss. It has more protein and healthy fats and less of carbs. Vegetarians get most of their proteins from lentils and legumes. Healthy fats include cheese, butter, coconut oil and olive oil.