A study in mice shows that a ketogenic diet, where you get most of your calories from fat, may cause diabetes (Journal of Physiology, August 8, 2018). A keto diet requires you to severely restrict carbohydrates and proteins, so your body uses fat as its main source of energy which produces large amounts of ketones. Eating mostly fat and severely restricting carbohydrates and proteins has been shown to help people lose weight in the short run, but long term studies fail to show that the weight loss is maintained (Exp Clin Cardiol, Fall 2004;9(3):200–205).
Definition of a Ketogenic Diet
On a keto diet, you have to restrict proteins as well as carbohydrates because certain protein building blocks can be converted to carbohydrates. Your body gets most of its energy from fat and when you burn mostly fat for energy, the fat is converted to ketones that are also used to fuel your energy needs. This is a protective mechanism to help keep you alive when you can't get enough food to meet your energy needs. When you are starving, your body releases fat from its fat stores, and you burn body fat for energy. Burning fat for energy releases large amounts of ketones that can also be used for energy to help prevent you from starving to death.
How a Keto Diet Might Increase Diabetes Risk
A keto diet may increase risk for developing diabetes by preventing your body from responding to insulin, presumably by causing fat to be deposited in the liver (Journal of Physiology, August 8, 2018). Nearly fifty percent of North American adults are already diabetic or have pre-diabetes (also called metabolic syndrome), and more than 30 percent of these people do not know it (JAMA, Sept 8, 2015;314(10)). Everyone's blood sugar normally rises after they eat. If blood sugar rises too high, it can cause sugar to stick to the outer membranes of cells throughout your body. Once stuck on a cell, sugar cannot get off and a series of chemical reactions eventually convert the sugar to sorbitol, which destroys that cell. To prevent blood sugar levels from rising too high, your pancreas releases insulin into the bloodstream, which lowers blood sugar by driving sugar from your bloodstream into your liver. However, if your liver is full of fat, it does not accept the sugar and blood sugar levels rise even higher. This is called insulin resistance.
In this new study, mice who were placed on a high-fat keto diet developed insulin resistance, higher blood sugar levels, and higher insulin levels than those placed on a high-fat and high-carbohydrate diet. This suggests that a keto diet might cause higher levels of markers of insulin resistance than the typical high-fat, high-sugar Western diet that is associated with the high incidence of diabetes and pre-diabetes. The authors conclude that "when fatty acids are metabolized, their products might have important signaling roles to play in the brain," and that "carbohydrate-restricted diets which limit our plant and fiber intakes have bad effects on our gut health."
On the other hand, an earlier one-year trial of a keto diet that was high in the good polyunsaturated and monounsaturated fats and low in saturated fats caused diabetics to lose substantial weight, lower their HbA1c that measures cell damage from diabetes, and lower fasting blood sugar (Am J Clin Nutr. Oct 2015;102(4):780-90).
• Keto diets can help people lose weight in the short term but have not been shown to help them keep that weight off long-term. For safe and prolonged weight loss, I recommend intermittent fasting.
• For some people, staying on a keto diet long term may increase liver fat so they are more likely to become insulin resistant and develop diabetes.
• If you choose to try a keto diet, try to restrict saturated fats (found in animal products) and eat mostly the good monounsaturated and polyunsaturated fats (found in plants). The most important dietary component to help prevent diabetes may well be soluble fiber found in all foods from plants.
• Whatever diet you choose to follow, I recommend eating a wide variety of vegetables, fruits, whole grains (not ground into flour), beans, nuts and other seeds, while restricting meats, sugar-added foods, sugared drinks and fried foods.