PhD student Chaitong Churuangsuk presents key points regarding both potential benefits and risks associated with following a low carbohydrate diet.
In a previous blog post, we talked about the importance of iodine in plant-based and vegan diets. Today, we will discuss low carb diets – which have grown in popularity over the past 30 years. Many are debating whether going ‘low carb’ is good or bad for health, but it is not quite clear whether everyone is talking about the same ‘low carb’ diet.
In this blog post, we refer to carbohydrates as the carbohydrate-rich foods that are regularly consumed by the population – this includes wholegrains, cereals, rice, bread, potatoes and pasta, as well as cakes, biscuits and sweets. As the quality of carbohydrates matters, not all sources of carbohydrates are the same and carbohydrates are not just sugar
What are low carb diets?
The popular definition of what a low carb diets is is unclear, with definitions differing between individuals. In our recent review, we found that there is no consensus definition of what a ‘low carb’ diet is. Some experts suggest a diet would be considered ‘low carb’ when carbohydrates contribute to less than 23% of the calories consumed each day, while very-low carb (ketogenic) diets feature carbohydrates contributing even less toward the energy (5-10% of calories) – or less than 50 grams per day.
Some people may decide to cut all sources of carbohydrates, while others adopt diets that only cut confectionaries and refined wheat products but keep in some wholegrains. The energy content of the diet may not always be changed, depending on amounts consumed, and the nutrient content (including vitamins and minerals) of the overall diet may change.
With carbohydrate-rich foods being cut, what foods can be eaten instead?
Some may choose meats, cheeses, butter and cream while others may choose beans, pulses, legumes, salmon and avocado. Either way, fat and protein are consumed in place of carbohydrates and these animal vs plant sources of fat and protein can have different impacts on health. Making good food choices is important to ensure that the full spectrum of nutrients is acquired from the diet. For example, fibre is present in foods besides wholegrain cereals – for example legumes (a cup of boiled lentil contains ~15 g of fibre) and fruit and vegetables (1 medium apple with skin contains 4-5 g of fibre, or one large avocado contains 6-7 g of fibre).
Is low carb good for weight loss?
Low carb diets work well for some people. Extensive scientific evidence supports that low carb diets are effective as a valid weight loss treatment. However, the longer the diet, the less effective it can become, as most people regain the weight they lost. This could be due to difficulties in adhering to the diet. Ultimately, there is no silver bullet, and people can have very different experiences when following the diet.
Can a low carb diet provide enough vitamins and minerals?
By substantially lowering or excluding carbohydrates from the diet, there is always an increased risk of vitamin and mineral insufficiencies or deficiencies. Carbohydrate-rich foods are a good source of vitamins and minerals (as shown in the table below). Cutting out carbs can result in lowering intakes of vitamin B1, folate, calcium, magnesium, and iron. There have also been case reports of acute thiamine deficiency in people following low carb diets (e.g. heart and neurological symptoms, and visual problem). It is critical to get the right information and gain knowledge to inform which foods should replace replace carbs. A consultation with a health professional can help, including your GP, or a registered dietitian who can support your lifestyle change. Supplementation should be considered for people who wish to pursue long-term low carb diets, ideally following discussion with a medical professional. In fact, in our recent survey, we found that only 1 in 10 low carb dieter took multi-vitamin supplements.
What are the effects of low carb diets on blood cholesterol?
Short term low carb diet (<1 year) often showed reduced fasted levels of triglycerides and increased level of HDL cholesterol, and this can be a beneficial change. On the other hand, low carb diets showed no improvement or increase in LDL cholesterol LDL-cholesterol levels (sometimes called ‘bad’ cholesterol that deposit in blood vessel and is linked to heart attack). This seems to depend on the type of food sources that are chosen to replace carbs. Low carb diets with high levels of saturated fatty acids, which mostly are from animal fat/protein (beef, pork), could increase LDL-cholesterol, while low carb diets with higher intakes of unsaturated fatty acids (plant/fish origin) show the opposite result with lower LDL-cholesterol. If you have concerns about your blood lipids, it is a good idea to visit your GP for some tests, especially if you plan to start a new diet.
Is there any long-term health effect of a low carb diet on heart disease?
Evidence of links between low carb diets and heart diseases or cardiovascular diseases (CVD) is limited to large observational population-based studies. The evidence points out that low carb diet is associated with higher chance of having heart disease, other atheroscleorotic diseases (e.g. stroke), abnormal heart beating, including risk of death from heart diseases. This may be due to nature of the data, with the possibility that people following the diets were at greater risk in the first place.
Few studies have shown that sources of protein and fat replacing carb might contribute to different impact on CVD. In the USA, men who followed a low carb diet pattern (carb <40% of energy intake), with high animal meat and fat had a higher risk of CVD, while women who followed a low carb diet with high plant protein/fat had a lower risk of CVD.
However, the above studies did not account for weight loss, which could have different impact on health. Weight loss in adults who are obese can improve risk factors for heart disease and prevent death from heart disease too.
Are there key steps to follow before switching to a low carb diet?
It depends on the motivations to follow the diet. To lose weight? To manage your diabetes? Or for general health improvement? It is important to consider whether the benefits will outweigh the risk.
Being able to adhere (stick) to the diet is important (in term of taste, affordability, and potential symptoms associated with changing the foods you usually consume). Having a good support network is also important, especially to get sound advice to support food choices – few people following low carb diets initiate a conversation with their GP, and potentially miss out on evidence-based support and referral to specialists.
If following a low carb diet turns out not to be possible, it is OK to choose a different diet. There are many weight loss diets with less extreme restrictions, which are also less likely to diminish vitamin and mineral intake. Cutting added sugar (e.g. sugar in tea / coffee, sweets and confectionary, and sweetened soda drinks) is a small step that is achievable, and can make a difference (including for oral health).
Limiting the amount of carbs consumed each day might help achieve a better glucose control for those with type 2 diabetes. Losing weight through diet is an essential factor in achieving better disease management, and a low carb diet can help achieving this. To date, there is no best diet recommended, in term of macronutrient composition, for diabetes management. The British Dietetic Association recommend support from a dietitian to ensure nutritional adequacy when following a low carb diet for type 2 diabetes management and weight loss.
To read more of our work on the topic
- Systematic review. Low-carbohydrate diets for overweight and obesity: a systematic review of the systematic reviews.
- Systematic review: Impacts of carbohydrate-restricted diets on micronutrient intakes and status: A systematic review.
- Observational study: Lower carbohydrate and higher fat intakes are associated with higher hemoglobin A1c: findings from the UK National Diet and Nutrition Survey 2008-2016.
- Review: Low and reduced carbohydrate diets: challenges and opportunities for type 2 diabetes management and prevention. (free link here)
- Survey: Carbohydrate knowledge, dietary guideline awareness, motivations and beliefs underlying low‑carbohydrate dietary behaviours’ (enhanced open access pdf here)
Chaitong Churuangsuk is a PhD student in the, School of Medicine (Human Nutrition) at the University of Glasgow. He supervised by Dr Emilie Combet and Prof Mike Lean. His research focusses on low carbohydrate diets in the management of obesity and type 2 diabetes, including the nutritional adequacy in relation to glucose metabolism of the low carbohydrate diets. Chaitong (Bir) has studied Medicine at the Faculty of Medicine, Prince of Songkla University (Thailand) and has a MSc in Human Nutrition with Specialisation in Clinical Nutrition from the University of Glasgow.