Ketogenic (keto) diet and heart

Ketogenic (or keto) diet has lately been a rage as the ultimate weight-reducing diet plan. The basis of this diet is to drastically reduce the carbohydrates in the diet → from 300g/day to < 50g/day. There is a corresponding increase in the fat and protein in the diet.

Figure 1: The keto diet pyramid

Carbs are the go-to fuel source for the body, but when they are in short supply the body switches to using fat instead, like a hybrid car switching from gas to electricity. The process of using fat as fuel generates water soluble ‘ketones’, hence the term ketogenic diet.

The breakdown of carbs in the body is very effective and complete, producing water and CO2 as by-products. On the other hand, fat breakdown is incomplete and leaves behind unused fuel in the form of ketones as leftovers, like food leftovers on a plate. The body discards this unused fuel as is, resulting in a net loss of calories. This is the basis of ketogenic diet.

Body naturally produces ketones during starvation or exercise, among other scenarios. 

What is keto diet?:

The figure 1 depicts the foods recommended in the keto diet. The general idea is to cut carbohydrates while supplementing with fats and proteins. For further recommendations and diet plans, please refer to the health guides available free on the internet.

Mechanism of effect:

Mechanism of effect is not known clearly but possibly related to:

  1. Feeling full early from the high fat and protein content
  2. Using protein or fat for energy is tedious for the body and causes weight loss through energy expenditure.
  3. Since glucose from diet is cut-off, body makes its own glucose which uses up calories. Some organs can only use glucose as fuel.
  4. Excess ketones suppresses appetite and reduces calorie intake

The good and the bad..

Five good things about the keto diet:

  1. Reduce weight up to 30lbs over 6 months → Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet
  2. Reduce bad cholesterol (LDL) and triglycerides while increasing the good cholesterol (HDL) → Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo.
  3. Reduce obesity around the abdomen and waist (up to 30% reduction in abdominal fat mass) 1
  4. Reduce systolic and diastolic blood pressure
  5. Increase the effect of intrinsic insulin in diabetes type 2

Five things to be careful:

  1. Participants in the reported research studies underwent strict behavioral therapy to follow the protocol. This means that the real-world results may be different.
  2. Consistent results were not noted beyond the first 6 months. The effects were either short-lived or the participants found the diet to be non-sustainable 2.
  3. At the start, people report feeling poor, generalized weakness and nausea. This is termed ‘keto flu‘ which can affect the motivation early on. Conversely, the long term effect of this diet on various organs, especially the liver and kidney are not known.
  4. Most carbohydrate rich foods are also rich in dietary fiber. Cutting these out increases the risk of diabetes and heart disease 3.
  5. The type of substituted protein and fat, whether plant-based or animal-based, is also important. A ketogenic diet supplemented by a high intake of animal-based protein and fat was not associated with a lower risk of heart disease, but rather with higher risk of death 4.

Keto diet and heart:

A diet which is rich in carbohydrates, especially refined sugars and fructose, is associated with a condition called metabolic syndrome. Metabolic syndrome constitutes of high blood pressure, high blood glucose, high cholesterol and excess fat around the waist. All these conditions together increase the risk of heart disease. Consequently, a diet with balanced carbohydrate intake and low processed sugars can reduce the risk of heart disease5.

The term ‘glycemic index’ is often used to describe the quality of carbohydrate in the diet 5. Glycemic index is a measure of how high the blood glucose goes after eating a particular foodstuff as compared to eating the same amount of pure glucose. Foods with lower glycemic index allow slower rise in glucose and also provide enough time for the body’s insulin to build up in response (figure 2). This prevents sudden spikes in blood glucose. The lower the glycemic index, the better the quality of glucose and insulin control. Thus, the quality of carbohydrate rather than the quantity is what matters the most.

Figure 2: Glycemic index in various food
Figure 2: Glycemic index in various food

Most beneficial effects with the keto diet are linked to the weight reduction and not the process of ketosis itself. Starting a diet regimen also results in behavioral changes, such as being mindful of the calories. In general, subtle but significant benefits were noted with the keto diet especially on the blood pressure and the waist circumference. Being regimental about one’s diet gives the ability to say no to processed food. 

There have been no studies suggesting direct benefit to the heart or prevention of heart disease. The effect on cholesterol levels is inconsistent in various studies. Also, the effect of altered fat metabolism in ketogenic diet on cholesterol plaque formation is not known. It is unknown if the diet truly help stop progression of heart blockages.

Another unknown variable is the effect on exercise capacity. Exercise is an essential part of maintaining a healthy heart. Some data suggests no change6, while others indicate increased fatigue and lack of motivation to exercise7. But largely these effects are dependent on the person and their motivation.

One last point, is ketogenic diet clearly superior to other weight loss diets? This has not been proven beyond doubt8. The essence of ketogenic diet is the ‘ketosis’ that results from the diet and the clear role of ketosis in the health benefits is not known. The effects were not consistently superior to a regular low-fat diet2. This is important as the ketogenic diet may be very hard to sustain, it requires extraordinary motivation and calls for significant compromises. This is the biggest factor where the diet fails, where the diet cannot be adopted by many or sustained for long.

In conclusion, ketogenic diet can have beneficial effects on the heart. Like any diet regimen, keto diet imparts a sense of purpose and there are people that vouch for its benefits. When coupled with exercise, a balanced carbohydrate diet is favorable to the heart.

The effect of salt in diet is explained on a different page.

The discussion above was to provide a simple understanding of keto diet and the effects on the heart. I would encourage a healthy discussion regarding the risks and benefits with your cardiologist and dietician. References are provided at the end of this page. The discussion is not all-inclusive or exhaustive and individual patient needs may vary. 

All opinions expressed here are those of the author and not of the employer. Information provided here is for medical education only. It is not intended as and does not substitute for medical advice.

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1.         Brinkworth GD, Noakes M, Buckley JD, Keogh JB, Clifton PM. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo. The American journal of clinical nutrition 2009;90:23-32.

2.         Nordmann AJ, Nordmann A, Briel M et al. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Archives of internal medicine 2006;166:285-93.

3.         Khaw KT, Barrett-Connor E. Dietary fiber and reduced ischemic heart disease mortality rates in men and women: a 12-year prospective study. American journal of epidemiology 1987;126:1093-102.

4.         Fung TT, van Dam RM, Hankinson SE, Stampfer M, Willett WC, Hu FB. Low-carbohydrate diets and all-cause and cause-specific mortality: two cohort studies. Annals of internal medicine 2010;153:289-98.

5.         McKeown NM, Meigs JB, Liu S et al. Dietary carbohydrates and cardiovascular disease risk factors in the Framingham offspring cohort. Journal of the American College of Nutrition 2009;28:150-8.

6.         Brinkworth GD, Noakes M, Clifton PM, Buckley JD. Effects of a low carbohydrate weight loss diet on exercise capacity and tolerance in obese subjects. Obesity (Silver Spring, Md) 2009;17:1916-23.

7.         White AM, Johnston CS, Swan PD, Tjonn SL, Sears B. Blood ketones are directly related to fatigue and perceived effort during exercise in overweight adults adhering to low-carbohydrate diets for weight loss: a pilot study. Journal of the American Dietetic Association 2007;107:1792-6.

8.         Naude CE, Schoonees A, Senekal M, Young T, Garner P, Volmink J. Low carbohydrate versus isoenergetic balanced diets for reducing weight and cardiovascular risk: a systematic review and meta-analysis. PloS one 2014;9:e100652.