The Truth About Low Carb Diets

Low-carbohydrate diets have been touted as the cure-all in nutrition. However, nutrition is complicated and one solution is not going to be the answer to everyone’s problems. So, how many of the claims about low-carb diets are true? Read on to find out.

What is a low-carb diet?

There are no firm guidelines defining what a low-carbohydrate diet is. Generally, a moderately low-carbohydrate diet consists of 150g of carbohydrates a day^[1,2]. This would mean carbohydrates make up 30% of someone's 2000kcal intake a day^[1]. Although, a diet could be considered low-carb if it contains as much as 45% carbohydrates^[3], as this is less than the 50% carbs that make up a typical Western diet^[4,5]. A very low-carbohydrate, or ketogenic diet consists of less than 50g of carbohydrates per day^[6]. You can find out more in our What is the Ketogenic Diet? article.

Low-carbohydrate diets can vary a lot from one to another. To achieve a low-carbohydrate diet, grains, starchy vegetables (such as potatoes), and fruits are reduced or eliminated entirely. This leads to a diet that is higher in fat and protein. Often, a low-carbohydrate diet contains animal products^[7], but it doesn’t have to.

Getting enough nutrients

A low-carbohydrate diet could help to reduce the amount of highly processed, unhealthy foods eaten. This is because they tend to be high in simple carbohydrates and fat^[8]. Carbohydrates and fat in the right proportion lead to foods which are high in calories, easy to overeat, and relatively low in vitamins and minerals^[9]. Therefore, by reducing the amount of carbohydrates in the diet, a person may, by default, achieve a healthier dietary pattern^[8].

On the flip side, eliminating foods from the diet can make it more difficult to consume certain nutrients, such as folate and iodine^[10]. Another nutrient that is often seen as a concern is fibre. Fibre, while technically a carbohydrate, is non-digestible and therefore treated differently than other digestible carbohydrates, like starch. The issue when following a low-carb diet in the West is the majority of the fibre eaten comes from grains^[11]. The good news is vegetables, seeds, and nuts are high in fibre whilst being low in digestible carbohydrates, so they are great foods to include in a low-carbohydrate regime. In fact, it’s been shown that a low-carbohydrate diet can provide at least the recommended amount for all nutrients,^[12] but this does require a bit of thought.

Losing weight

It’s a common myth that carbohydrates are what cause people to gain weight^[13]. This leads to the idea that low-carb diets are superior for weight loss.

When looking at low-carbohydrate diets versus diets higher in carbohydrates, it appears that in the short term, a lower carbohydrate intake can lead to a greater weight loss^[14]. However, from six months and beyond, there is little difference in the amount of weight lost when comparing diets that vary in carbohydrates^[14-16]. Part of the reason for this is that people gradually increase their carbohydrate intake over time, which results in more calories being eaten^[16]. A key factor for success in these studies was adherence^[16]. The better a person can stick to their chosen diet, whatever that may be, the greater their chance of reaching their goals^[16].

To find out more about carbohydrates in relation to weight loss and in general, check out our article here.

Is a low-carb diet right for me?

A low-carbohydrate diet may be the right choice for some people. It’s simple to follow but like any diet, the quality of foods eaten should still be considered.

It has been shown that a low-carbohydrate diet can increase LDL (bad) cholesterol and that this effect is greater for certain individuals^[17]. Therefore, it’s a good idea to keep an eye on cholesterol levels during doctor check-ups in the early stages of a low-carb diet. It’s best to aim for unsaturated fats over saturated fats, which have been shown to be more beneficial in relation to cardiovascular health^[18-20].

What is more important to think about than low-carb, high-carb, or single nutrients is the overall diet^[21,22]. This means focusing on the types of carbohydrates and fat being eaten, and the foods supplying them, rather than the amounts. Aiming for a whole-food, plant-rich diet is one way to achieve this.

References

1. Patel K. Does “low-carb” have an official definition? Date Accessed: 15/12/2020. [Available from: https://examine.com/nutrition/does-low-carb-have-an-official-definition/]
2. Wylie-Rosett J, et al. Health effects of low-carbohydrate diets: where should new research go? Curr Diab Rep. 2013; 13(2):271-8.
3. Hu T, et al. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials. American journal of epidemiology. 2012; 176 Suppl 7(Suppl 7):S44-S54.
4. England PH. NDNS results from years 1 to 9. London, UK: PHE Publications. 2019.
5. Statistics NCfH. CDC. Dietary intake for adults aged 20 and over. Date Accessed: 15/12/20. [Available from: https://www.cdc.gov/nchs/fastats/diet.htm]
6. Uppaluri WMK. Ketogenic Diet. StatPearls, (eds). Treasure Island (FL); 2019.
7. Guess N. Dietary intake in people consuming a reduced-carbohydrate diet in the National Diet and Nutrition Survey. Journal of Human Nutrition and Dietetics. 2017; 30(3):360-8.
8. Martínez Steele E, et al. The share of ultra-processed foods and the overall nutritional quality of diets in the US: evidence from a nationally representative cross-sectional study. Popul Health Metr. 2017; 15(1):6-.
9. Hall KD, et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019; 30(1):67-77.e3.
10. Churuangsuk C, et al. Impacts of carbohydrate-restricted diets on micronutrient intakes and status: A systematic review. Obesity reviews : an official journal of the International Association for the Study of Obesity. 2019; 20(8):1132-47.
11. Stephen AM, et al. Dietary fibre in Europe: current state of knowledge on definitions, sources, recommendations, intakes and relationships to health. Nutrition Research Reviews. 2017; 30(2):149-90.
12. Zinn C, et al. Assessing the nutrient intake of a low-carbohydrate, high-fat (LCHF) diet: a hypothetical case study design. BMJ Open. 2018; 8(2):e018846-e.
13. Huel. Why Carbs Aren’t Bad. Date Accessed: 03/01/2020. [Available from: https://eu.huel.com/pages/why-carbs-arent-bad]
14. Guo J, et al. Objective versus Self-Reported Energy Intake Changes During Low-Carbohydrate and Low-Fat Diets. Obesity (Silver Spring, Md). 2019; 27(3):420-6.
15. Das SK, et al. Long-term effects of 2 energy-restricted diets differing in glycemic load on dietary adherence, body composition, and metabolism in CALERIE: a 1-y randomized controlled trial. The American journal of clinical nutrition. 2007; 85(4):1023-30.
16. Gardner CD, et al. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. Jama. 2018; 319(7):667-79.
17. Kirkpatrick CF, et al. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of Clinical Lipidology. 2019; 13(5):689-711.e1.
18. Clifton PM, et al. A systematic review of the effect of dietary saturated and polyunsaturated fat on heart disease. Nutr Metab Cardiovasc Dis. 2017; 27(12):1060-80.
19. Forouhi NG, et al. Dietary fat and cardiometabolic health: evidence, controversies, and consensus for guidance. BMJ (Clinical research ed). 2018; 361:k2139-k.
20. Liu AG, et al. A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutr J. 2017; 16(1):53-.
21. Reynolds A, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet. 2019; 393(10170):434-45.
22. Bao W, et al. Low Carbohydrate-Diet Scores and Long-term Risk of Type 2 Diabetes Among Women With a History of Gestational Diabetes Mellitus: A Prospective Cohort Study. Diabetes care. 2016; 39(1):43-9.
23. Marten B, et al. Medium-chain triglycerides. International Dairy Journal. 2006; 16(11):1374-82.