Ketogenic Diet and Lipids

Historically a ketogenic diet was used as early as the 1920s to treat epilepsy in children. More recently it has become popular as a way to lose weight and has been promoted for the management of Type II Diabetes.

What is a Ketogenic Diet?

This diet severely restricts carbohydrates, typically providing only 5-10% of calories (about 20-50g/ day - the amount you’d find in 2-3 slices of bread), compared to the 50% currently recommended. It also includes moderate levels of protein (approximately 10% of calories) with no restriction of fat (70-80% of calories).

The idea behind the ketogenic diet is to use fat as a fuel source rather than carbohydrates, which is the body’s preferred source of fuel. This process produces ketones. Ketosis occurs when these ketone bodies accumulate in the blood. Exact quantities of carbohydrates to induce ketosis will vary, as achieving ketosis is highly individualised.

Many types of ketogenic diets exist, but all ban carb-rich foods such as sweet sugary foods, breads, cereals, pasta, rice, potatoes and other starchy vegetables and fruit juices. But also foods like beans and legumes, and most fruits.  Most ketogenic diets allow foods high in saturated fat and cholesterol, such as fatty cuts of meat, processed meats, lard, butter, cream, and cheese, as well as sources of unsaturated fats, including nuts, seeds, avocados, plant oils, and oily fish.

As a result, a ketogenic diet can end up being high in saturated fat and cholesterol, and low in foods which we know are cardio-protective e.g. legumes, whole grains, fibre-rich starchy vegetables and most fruits.

The Effect of a Ketogenic Diet on Weight and Cardiometabolic Risk Factors.

Because of the increasing popularity of the ketogenic diet, the US National Lipid Association Nutrition and Lifestyle Task Force recently reviewed the evidence and published a scientific statementⁱ on the effect of these types of diets on body weight and cardiometabolic risk factors, including lipids. They concluded:-

• Very low carbohydrate diets are not superior to other dietary approaches for weight loss and are difficult to maintain in the long term.
• They may have some advantages related to appetite control, triglyceride reduction and reduction in the use of medication in Type II Diabetes management. BUT only in the short term, as longer-term studies have not been conducted.
• Studies have shown mixed effects on LDL-C levels, with some studies showing an increase. This appears to be related to the saturated fat content of the diet.
• Some individuals experience extreme effects of a ketogenic diet on LDL-C and this may be related to genetic factors. For this reason the National Lipid Association expressed concern for ketogenic diets being used by people with hypercholesterolaemia, particularly Familial Hypercholesterolaemia. They concluded that this diet is contraindicated for these conditions.
• The Ketogenic Diet is also contraindicated in patients with severe hypertriglyceridaemia due to genetic or acquired causes of lipoprotein lipase dysfunction
• There’s no clear evidence for advantages on other cardiometabolic risk markers
• There’s minimal data regarding the long-term safety and efficacy (> 2 years).
• According to findings from observational studies, very low carbohydrate diets are associated with an increased risk of cardiovascular mortality.

It’s also worth noting this diet has been associated with short term side effects such as gastrointestinal complaints including constipation, nausea, and abdominal pain which are often experienced in the first few weeks. Some individuals may experience symptoms described as the ‘keto flu’ within 2 to 4 days of starting a keto diet, which may occur as the body adapts to using ketone bodies for fuel. It may last a few days to one week and include light-headedness, dizziness, fatigue, difficulty exercising, poor sleep and constipation.

In Summary

The effect of the ketogenic diet on long term cardiovascular risk remains unknown. It challenges the current nutrition recommendations from various organisations such as Public Health England (PHE)ⁱⁱ, The National Institute for Health and Care Excellence (NICE)^iii,iv and the recent European Society of Cardiology/ European Atherosclerosis Society guidelines for the management of dyslipidaemias^v as it severely restricts or eliminates foods associated with cardio-protective benefits, and encourages a high intake of foods known to increase risk, such as foods high in saturated fat.

The most important way to prevent CVD is to promote a healthy lifestyle throughout the life span. Cardio-protective dietary patterns emphasise eating vegetables, fruits, nuts, whole grains, vegetable proteins, lean animal protein and fish and minimise the intake of saturated fats, processed meats, refined carbohydrate foods and foods with added sugars and sweetened drinks.

[i] 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
Kirkpatrick, Carol F. et al. Journal of Clinical Lipidology, Volume 0, Issue 0. https://www.lipidjournal.com/article/S1933-2874(19)30267-3/fulltext

[ii] The Eatwell Guide: https://www.gov.uk/government/publications/the-eatwell-guide

[iii] NICE Guideline: Familial hypercholesterolaemia: identification and management. Clinical Guideline (CG71)
 
[iv] NICE Guideline: Cardiovascular disease: risk assessment and reduction, including lipid modification. Clinical guideline [CG181]
 
[v] François Mach, Colin Baigent, Alberico L Catapano, et al ESC Scientific Document Group, 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk: The Task Force for the management of dyslipidaemias of the European Society of Cardiology (ESC) and European Atherosclerosis Society (EAS), European Heart Journal, , ehz455, https://doi.org/10.1093/eurheartj/ehz455