The ketogenic (or “keto”) diet is all the rage because of its touted weight loss benefits, but given the high proportion of fat in this diet, have you ever wondered whether it’s good for your heart?

What is the ketogenic diet and how does it work?

The ketogenic diet involves drastically reducing your intake of carbohydrates and replacing it with fat. A standard ketogenic diet typically contains 75% fat, 20% protein and only 5% of carbohydrates. Normally, the body’s preferred fuel source is glucose, which is the easiest molecule for it to turn into energy. Glucose comes from the carbohydrates that we eat (starches and sugars). However, when we consume too much carbohydrates, more than what we need for energy, the excess glucose gets stored in the liver as glycogen, and any excess beyond that is stored as fat. Excess fat is associated with obesity and contributes to the development of conditions like pre-diabetes, diabetes and heart disease.

Because the ketogenic diet is so low in carbohydrates, the body has to turn to an alternative energy source – fat. To generate energy, stored fat is broken down into ketones, in a process known as ketosis. If carbohydrate supplies are not replenished, the body will continue to keep burning your body’s fat reserves for energy.

What does the ketogenic diet involve?

This diet is very low in carbohydrates and people on this diet will generally eat less than 50 grams of carbohydrates in a day. This means that foods containing a lot of carbohydrates, such as sugary foods and drinks, pastas, breads, rice, grains, most fruit, starchy and root vegetables (e.g. potatoes, beets, carrots) and beans or legumes, will need to be avoided.

So what can be eaten? Here’s a list of foods typically consumed in a keto diet:

• Meats e.g. poultry, pork
• Fatty fish e.g. salmon, tuna, trout
• Leafy green vegetables, cauliflower, broccoli, eggplant, cucumber
• Tomatoes, mushrooms, onions
• Dairy (grass-fed if possible) e.g. eggs, butter, cream, cheese, Greek yoghurt
• Unsweetened dairy substitutes e.g. coconut, almond, cashew, soy milk
• Avocadoes
• Low-glycaemic berries e.g. raspberries, blueberries, blackberries
• Healthy oils e.g. olive, coconut, flaxseed, grapeseed, hempseed
• Nuts and seeds e.g. almonds, walnuts, flax seeds, chia seeds, etc.

What are the benefits and risks of a ketogenic diet?

The ketogenic diet has been shown to be effective in weight loss, possibly because of calorie restriction and reduced hunger. However, the longer-term sustainability of weight loss has yet to be well studied. Because the ketogenic diet involves the body burning fat for fuel, going on this diet can also help you lose excess body fat. As excess body fat has been linked to insulin resistance, which contributes to pre-diabetes and diabetes, ketogenic diets can improve insulin sensitivity. Combined with the lower intake of carbs, the ketogenic diet can help to improve blood sugar control in people with diabetes and pre-diabetes. Studies have shown that low-carbohydrate and high-fat diets in overweight patients with type 2 diabetes can achieve weight loss, lower blood sugar levels, improved glucose control and increased insulin sensitivity^1-4.

However, the ketogenic diet also comes with risks. Firstly, the ketogenic diet is high in fat, so if a lot of the consumed fat is of the saturated fat variety, then there is a potential for increased LDL (“bad”) cholesterol levels, which is a risk factor for heart disease. Secondly, the ketogenic diet is extremely low in certain nutrients-packed fruits, vegetables, grains, and legumes, which means that people on the diet may be at risk for deficiencies in key micronutrients (e.g. vitamins B and C, magnesium, potassium, phosphorus) as well as have insufficient fibre intake, which can lead to constipation and other longer term effects on the gut, heart and immune system. Thirdly, a diet high in animal protein increases the excretion of calcium and oxalate in the urine. This can make you more susceptible to kidney stones. Animal proteins are also purine-rich foods. Purines are broken down to uric acid when metabolised, and a build-up of uric acid in the blood can lead to gout.

  Is the ketogenic diet good for your heart? 

You might have heard that eating fatty foods is bad for the heart and increases the risk of high cholesterol, high blood pressure and heart attacks. So what is the impact of a ketogenic diet on heart health? Firstly, it’s important to stress that if you are thinking of going on a ketogenic diet, you should make sure that the fats you eat are primarily of the healthy monounsaturated or polyunsaturated variety. You should reduce your intake of fatty foods that contain saturated fat or trans fat (e.g. fast food, fatty meats, processed foods such as commercially prepared cookies, cakes, crackers and chips) as these have been linked to poor heart health and obesity.

Secondly, there haven’t been any large scale studies on the longer-term effect of the ketogenic diet on heart health. Most studies so far have been smaller scale, of shorter duration, and have shown mixed results. In some studies, participants on the ketogenic diet showed improvements in risk factors for heart disease, like lowered blood pressure, blood sugar and body fat. On the other hand, other studies have shown that the ketogenic diet in diabetics was associated with elevated LDL cholesterol and triglyceride levels, which increase the risk for heart disease⁵. One recent study observed unexpected damage to blood vessels as the body’s metabolic response to a sudden rise in blood sugar, after seven days of ketogenic diet in nine healthy young males⁶. This finding suggests that those with poor cardiovascular health and who are considering going on a ketogenic diet should first discuss the potential benefits versus risks with their healthcare team.

Should I go on a ketogenic diet?

A ketogenic diet is not easy to follow and may be difficult to sustain for a long period of time. While the ketogenic diet may be useful for certain individuals e.g. people with type 2 diabetes and excess weight, it is important to discuss with your healthcare team before starting the diet, especially if you have chronic medical conditions. Medications used to treat type 2 diabetes may need to be adjusted if you are starting the diet. Your healthcare team may also need to monitor you closely for any side effects. In general, while diets such as the ketogenic diet could help to kickstart your journey towards better eating habits, a longer-term sustainable and balanced diet comprising whole grains, lean meats, fish, nuts, seeds, healthy oils, and lots of fruits and vegetables, with reduced consumption of refined carbohydrates and foods high in saturated or trans fat, will help you achieve and maintain your health goals of feeling well and looking good too!

References:

[1] Krebs JD, Bell D, Hall R, Parry-Strong A, Docherty PD, Clarke K, Chase JG. Improvements in glucose metabolism and insulin sensitivity with a low-carbohydrate diet in obese patients with type 2 diabetes. J Am Coll Nutr. 2013;32(1):11-17. [2] Yancy WS Jr, Foy M, Chalecki AM, Vernon MC, Westman EC. A low-carbohydrate, ketogenic diet to treat type 2 diabetes. Nutrition & Metabolism. Dec 2005, 2(1):34. [3] Westman EC, Yancy WS Jr, Mavropoulos JC, Marquart M, McDuffie JR. The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutrition & Metabolism Dec 2008, 5:36. [4] Kosinski C, Jornayvaz FR. Effects of Ketogenic Diets on Cardiovascular Risk Factors: Evidence from Animal and Human Studies. Nutrients 2017;9(5):517. [5] Leow ZZX, Guelfi KJ, Davis EA, Jones TW, Fournier PA. The glycaemic benefits of a very-low-carbohydrate ketogenic diet in adults with Type 1 diabetes mellitus may be opposed by increased hypoglycaemia risk and dyslipidaemia. Diabetic Medicine. 2018, 35(9):1258-1263. [6] Durrer C, Lewis N, Wan Z, Ainslie PN, Jenkins NT, Little JP. Short-Term Low-Carbohydrate High-Fat Diet in Healthy Young Males Renders the Endothelium Susceptible to Hyperglycemia-Induced Damage, An Exploratory Analysis. Nutrients. 2019;11(3):489.