Low Carb Diets and Why They Work

For the last 40 years at least, the command to eat less fat and more carbohydrate has dominated advice on healthy eating.

From the start, however, scientists raised doubts about its validity. As long ago as 1972, the renowned British nutritionist Professor John Yudkin, in his book ‘Pure, White and Deadly’, argued that it was sugar, not fat, that drove arterial disease.1

His work was roundly condemned by the processed food industry and, over the years that followed, consumption of carbohydrates – particularly processed and sugary carbohydrates – grew, while fat consumption declined.2

Obesity rates, meanwhile, have rocketed. In England today, 64 per cent of adults are overweight or obese3 and an estimated one in three adults in the UK are pre-diabetic.4

And yet almost half (48 per cent) of British adults surveyed in 2016 said that they had tried to lose weight over the previous year.5 High-carb, low-fat diets – still the standard advice given by many GPs6 – aren’t working.

Low fat and high carb: a recipe for poor health

Worse: they are doing harm. High-carb diets can worsen your blood fats, damage blood vessels and nerves, and lock you into a state of permanently elevated insulin. Over time, this leads to type 2 diabetes, and can even increase your risk of developing cancer. Eating a diet high in carbs also exposes your brain and body to highly addictive foods, making it difficult to develop healthy portion control.

Low carb v high carb diets

Carbs: how low should you go?

Could a high-fat, very low-carb diet be the answer instead? Plenty of celebrities seem to think so. “Keto” diets, or diets in which fat supplies as much as 90 per cent of calories, count Kim Kardashian and Megan Fox among their fan-bases.

Unfortunately for keto promoters, medical evidence suggests that over the long term, following a keto diet could be seriously harmful. Studies following up the health of people who have switched permanently to keto show a greater incidence of fatty liver, kidney stones7, bone fractures8 and vitamin and mineral deficiencies.9

The Mediterranean-style low-carb diet: key to good health

Key features of a Mediterranean-style low-carb diet

  • Slow-release glucose
  • High fibre
  • Healthy fats

If high-carb and keto are both risky, what is the safest way to lose weight?

Fortunately, we already have the answer to this. The traditional Mediterranean-style diet, based on unprocessed carbs, healthy fats, fresh vegetables and fruit, has been granting long life and good health for many centuries, and – studies show – is still doing so today.10

Slow glucose release for steady blood sugar

The Mediterranean-style diet is built around unprocessed, whole foods. Legumes, brown rice, barley, oats, buckwheat and rye break down slowly in the body, releasing energy steadily through the day.

By contrast, a high-carb diet subjects your cells to frequent sugar spikes. In response, your body releases insulin. However, over time, your body will become less and less sensitive to insulin, leading ultimately to type 2 diabetes – and from there, an increased risk of an array of poor health outcomes including heart attacks, stroke and kidney disease.

Additionally, we now know that in the presence of insulin resistance, increased blood sugar is a powerful driver of raised triglycerides – one of the most dangerous types of blood lipids (2).

Sugar spikes can also drive cancer progression. By taking up glucose, cells activate pathways that cancer cells can also use in order to divide and grow. Also, elevated insulin drives up levels of a chemical known as IGF-1, which is critical to tumour growth. A diet high in sugar and processed carbohydrate may be a risk factor in particular for breast cancer.11

Increased fibre

As well as keeping your blood sugar steady, a Mediterranean-style low carbohydrate regime is high in fibre. This helps you to feel fuller for longer.

High-carbohydrate diets do the opposite. Trying to restrict your intake of high-carb, low-fat food is a bit like trying to run up an escalator rolling downwards: you are eating foods that stimulate your appetite, while attempting to curb it. This is because the human body is primed to crave foods that contain twice as much carbohydrate as fat. In fact, scientists have gone as far as to identify this ratio as a defining feature of addictive foods.12

Fibre also counters insulin resistance, can provide protection against bowel cancer, and – last but not least – feeds the “good” bacteria that live in your guts, contributing to improved mood.13 There’s no doughnut anywhere that can do all of that.

Healthy fats, the Mediterranean way

From the day you start on a healthy low-carb diet, you will feel the benefit of lower blood sugar and better gut health. The rewards, though, don’t stop there. Because your diet is lower in carbohydrate, a greater proportion of your energy will come from fats. And because the fats that you consume are healthy fats, your long-term health prospects will improve greatly. Here’s why.

The power of olive oil

Olive oil is rich in antioxidants. Studies have linked their intake to a lowered incidence of cardiovascular disease, DNA damage, inflammation and blood clotting.

Perhaps the most well-researched antioxidant present in olive oil is a substance known as oleuropein. Responsible for the bitter taste in olive oil, oleuropein has been shown to have cholesterol-lowering and anticancer effects. The evidence from population studies bears this out, with a lower incidence of certain cancers in the Mediterranean area. Further evidence also suggests that oleuropein may be able to help protect against Parkinson’s disease and Alzheimer’s.14

Why omega-3 oils are critical to good health

A low-carb diet, then, is about much more than simply cutting back on carbs – it is also about taking in healthy fats.

As well as being rich in olive oil, a healthy Mediterranean-style diet also contains a high supply of omega-3 oils. Especially abundant in marine food, omega-3 oils work in the body to counter inflammation. This leads to a very wide range of better health outcomes, including a lowering of the risks of high blood pressure, raised “bad” cholesterol and raised sugar15, as well as improved mood16 and better memory.17

Freedom from “danger fats”

By putting value on healthy fats, rather than placing all fats in the “occasional treats” category, a Mediterranean-style low-carb diet will also protect you against fats that can do you harm.

Industrially-processed hydrogenated fats, or “trans” fats, are perhaps the most dangerous of all. Commonly added to high-carb foods such as pastries, biscuits and crackers, hydrogenated – or “trans” fats – are very harmful to human health, even in very small amounts.18

So overwhelming, in fact, is the medical evidence against them, that six European countries – Denmark, Norway, Austria, Hungary, Iceland and Switzerland – have banned their sale altogether.

Saturated fat, when consumed to excess, can also be unhealthy, and is linked particularly to an increased risk of colonic cancer.19

Low-carb diets and the future of medicine

More and more, medical professionals are starting to see the benefits of using a healthy, low-carb diet as a clinical intervention. A sensible way to put this into practice has been developed and tested by Dr David Unwin, a GP in Southport, who tweets as @lowcarbGP.

David, winner of the NHS Innovator of the Year 2016 award, advises his overweight patients to try to cut out sugar and cut down on white (easily digestible) carbs such as bread, pasta and rice. He recommends eating plenty of blueberries, strawberries and raspberries, which are relatively low in fruit sugar, and green vegetables, protein, butter, full-fat yogurt and olive oil to retain fullness.

In a recently published study20, patients following his advice lost almost 1½ stone on average, and 6 inches around the waist. There were big improvements in blood pressure and cholesterol levels too, and many of those with type 2 diabetes were able to come off medication. Patients on his diet also experienced a marked improvement in liver function. As non-alcoholic fatty liver disease is a known complication of obesity, this further benefits their health now and in the future. Dr Unwin’s GP practice is now saving more than £38,000 a year on its diabetes drug budget alone. Not bad for a diet that follows the science, not the rules of the old school.

Low-carb, not low-fat: five practical steps

  1. Avoid processed carbohydrates, and always check the label for added sugar. This includes fructose, glucose, maltose and other ingredients ending in “–ose”. Also avoid syrups and juices, either as ingredients or as beverages.
  2. Instead, go low and go slow: choose legumes, brown rice, oats, rye, barley and other wholegrains.
  3. Cook, cool and reheat carbs like pasta, potatoes and rice. If cooled and frozen quickly after cooking, rice keeps especially well in the freezer and can be defrosted in minutes.
  4. To succeed on a low-carb diet, increase your intake healthy fats. Focus, in particular, on foods rich in olive oil and omega-3 oils.
  5. Avoid all trans fats, including margarine. Food labels also sometimes term these “partially hydrogenated fats”. Eat saturated fats in moderation only.

  1. Yudkin, J. (1972). Pure, white and deadly: the problem of sugar. London: Davis-Poynter Ltd, cited in Mosley, M. (2016, May 23), Telegraph Online,‘5:2 author Michel Mosley: ‘I’m proof low-fat diets don’t work’ available at https://www.telegraph.co.uk/health-fitness/nutrition/52-author-michael-mosley-im-proof-low-fat-diets-dont-work 
  2. Ludwig, D.S., Willett W.C., Volek J., Neuhouser M.C. (2018), Dietary fat; from foe to friend? Science 16 Nov 2018: Vol 362 Issue 6416 pp 764-770 doi 10.1126/science.aau2096, available at https://science.sciencemag.org/content/362/6416/764
  3. NHS Digital (2019), Statistics on Obesity, Physical Activity and Diet, England, 2019, available at https://digital.nhs.uk/data-and-information/publications/statistical/statistics-on-obesity-physical-activity-and-diet/statistics-on-obesity-physical-activity-and-diet-england-2019/part-3-adult-obesity
  4. Mainous A.G., Tanner R.J., et al (2014), Prevalence of prediabetes in England from 2003 to 2011: population-based, cross-sectional study, BMJ Open 2014;4:e005002. doi: 10.1136/bmjopen-2014-005002, available at https://bmjopen.bmj.com/content/4/6/e005002.citation-tools
  5. Moss, R. (2016, March 10), ‘Two thirds of Brits are on a diet ‘most of the time’, Huffpost, available at https://www.huffingtonpost.co.uk/2016/03/10/majority-brits-are-on-a-diet-most-of-the-time_n_9426086.html
  6. NHS UK (2019), ‘Eat well: eating a balanced diet’, available at https://www.nhs.uk/live-well/eat-well/
  7. Arslan, N., Guzel, O. et al (2016), Is ketogenic diet treatment hepatotoxic for children with intractable epilepsy? Seizure 2016 Dec;43:32-38. doi: 10.1016/j.seizure.2016.10.024. available at https://www.ncbi.nlm.nih.gov/pubmed/27866088
  8. Uramek-Koziel M., Plute R., Bogneka-Kolka A, Czaczwar S.J. (2016), To treat or not to treat drug-refractory epilepsy by the ketogenic diet? That is the question, Ann Agric Environ Med. 2016;23(4):533–536 doi: https://doi.org/10.5604/12321966.1226841, available at http://www.aaem.pl/To-treat-or-not-to-treat-drug-refractory-epilepsy-by-the-ketogenic-diet-That-is-the,72465,0,2.html
  9. Bergqvist A.G., Chee C.M. et al (2003), Selenium deficiency associated with cardiomyopathy: a complication of the ketogenic diet, Epilepsia. 2003 Apr;44(4):618-20, available at https://www.ncbi.nlm.nih.gov/pubmed/12681013
  10. Dinu M., Pagliai G., Casini A., Sofi F. (2018), Mediterranean diet and multiple health outcomes: an umbrella review of meta-analyses of observational studies and randomised trials, Eur J Clin Nutr. 2018 Jan;72(1):30-43. doi: 10.1038/ejcn.2017.58. available at https://www.ncbi.nlm.nih.gov/pubmed/28488692
  11. Strober J.W. and Brady M.J. (2019), Dietary Fructose Consumption and Triple- Negative Breast Cancer Incidence, Front Endocrinol (Lausanne) 2019 Jun 12;10:367. doi: 10.3389/fendo.2019.00367, available at https://www.ncbi.nlm.nih.gov/pubmed/31244777
  12. Schulte EM, Avena NM, Gearhardt AN (2015) Which Foods May Be Addictive? The Roles of Processing, Fat Content, and Glycemic Load. PLOS ONE 10(2): e0117959 doi: https://doi.org/10.1371/journal.pone.0117959 available at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117959
  13. Thompson S.V., Hannon B.A., An, R., Holscher H.D. (2017), Effects of isolated soluble fiber supplementation on body weight, glycemia, and insulinemia in adults with overweight and obesity: a systematic review and meta-analysis of randomized controlled trials, The American Journal of Clinical Nutrition, Volume 106, Issue 6, December 2017, Pages 1514–1528, doi: https:///doi.org/10/3945/ajcn.117.163246, available at https://academic.oup.com/ajcn/article/106/6/1514/4823179?ijkey=86237911767cfc1c68ecd796ac2383c469294143&keytype2=tf_ipsecsha
  14. Gouvinhas, I., Machado, N., et al (2017). Critical Review on the Significance of Olive Phytochemicals in Plant Physiology and Human Health. Molecules (Basel, Switzerland), 22(11), 1986. Doi: 10.3390/molecules22111986, available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6150410/
  15. Kim, Y. S., Xun, P., Iribarren, C., et al (2016). Intake of fish and long-chain omega-3 polyunsaturated fatty acids and incidence of metabolic syndrome among American young adults: a 25-year follow-up study. European journal of nutrition, 55(4), 1707–1716 doi: 10.1007/s00394-015-0989-8, available at https://www.ncbi.nlm.nih.gov/pubmed/26816031
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  19. Reddy, B.S., (2002), Types and amount of dietary fat and colon cancer risk: Prevention by omega-3 fatty acid-rich diets Environ Health Prev Med. 2002 Jul; 7(3): 95–102. doi: 10.1265/ehpm.2002.95 available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2723490/
  20. Saslow, L. R., Summers, C., Aikens, J. E., & Unwin, D. J. (2018). Outcomes of a Digitally Delivered Low-Carbohydrate Type 2 Diabetes Self-Management Program: 1-Year Results of a Single-Arm Longitudinal Study JMIR diabetes, 3(3), e12. doi:10.2196/diabetes.9333, available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6238840/