Historically used in the treatment of medical conditions such as diabetes and epilepsy, “keto” is now rapidly gaining popularity as a weight loss strategy. It has also been associated with other beneficial health effects such as an improved blood lipid profile, reduced blood pressure, and greater mood stability. But what exactly is the ketogenic diet, and how does it work? Let’s take a look.
What is it?
The Institute of Medicine has traditionally recommended a macronutrient breakdown of 45-65% of calories from carbohydrate, 20-35% from fat, and 10-35% from protein. The ketogenic diet, on the other hand, typically consists of 5-10% of calories from carbohydrate, 70-80% from fat, and 10-20% from protein. For a standard 2,000 calorie diet, this works out to be about 40 grams of carbohydrate (2 small bananas), 165 grams of fat (12 tablespoons of oil), and 75 grams of protein (3 3-oz cooked chicken breasts). Some followers are even stricter with their carbohydrate intake, limiting it to only 20 grams per day.
The idea behind the ketogenic diet is that drastically cutting carbs forces the body to burn fat as fuel. Glucose, which comes from dietary carbohydrate, is the primary source of energy for the body’s cells. When dietary carbohydrate is not readily available (i.e. in an overnight fast), the body pulls stored glucose in the form of glycogen from the liver and then from the muscles. There is usually enough stored glucose for the body to sustain itself for 3 to 4 days. Beyond this, it transitions into using stored fat for energy, producing molecules called ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) as by-products. This physiological state is called ketosis. Whereas other popular diets such as Atkins also limit carbohydrate intake, the ketogenic diet is unique because it specifically increases fat intake while keeping protein intake moderate. This is because amino acids, which are the building blocks of proteins, can be converted to glucose, but fatty acids cannot.
How does it work?
There are several theories as to why the ketogenic diet may promote weight loss. Followers often report increased satiety and reduced hunger, possibly due to the higher fat content of the diet and favorable effects of ketones on appetite-stimulating hormones. Ketogenic diets are also associated with lower levels of insulin, a hormone that is released in response to carbohydrate intake in order to facilitate the uptake of glucose into cells. Proponents of a theory known as the carbohydrate-insulin model of obesity hypothesize that a high intake of refined carbohydrates and resultant high insulin levels promotes the storage of energy in fat cells, leading to overweight and obesity. Some research comparing high-carbohydrate and low-carbohydrate diets has indicated that individuals consuming low-carbohydrate diets require fewer calories to maintain their weight.
What are the drawbacks?
Negative side effects of severely reducing carbohydrate intake may include fatigue, irritability, and headaches. However, these symptoms often ease once the body adapts to burning fat for fuel. People following a ketogenic diet also sometimes report a “fruity” breath odor, which is caused by the elimination of acetone via respiration in the lungs. A longer-term possible side effect is multiple nutrient deficiencies as a result of low diet variety. Although it eliminates many unhealthy foods (such as refined carbohydrates, sugary snacks, and many processed foods), the ketogenic diet also limits nutrient dense foods such as legumes, most fruits, and many vegetables. This can make it difficult to get enough fiber, which is important for bowel regularity, appetite regulation, and a reduced risk of many chronic diseases.
What don’t we know?
More information is needed about the lasting effects of the ketogenic diet. In particular, researchers are focusing on how it impacts long-term metabolic health, bone density, and energy levels, as well as its safety and usefulness for people with different pre-existing medical conditions. We also need to better understand its implications for growth and development, as younger individuals are starting to try it. Finally, it will be important to assess its feasibility as a true lifestyle change by assessing adherence; because the ketogenic diet eliminates so many foods, many people may have trouble sticking with it in the long run.
Final thoughts
I’m intrigued by the ketogenic diet. Personally, I’ve found that I experience fewer cravings and have an easier time maintaining my weight when I eat a low-carb diet, and I think that the carbohydrate-insulin model of obesity makes a lot of sense. I’m also an advocate for food providing both health and pleasure, and am concerned about how restrictive the ketogenic diet is for both physical and psychological health. If you are a healthy adult interested in losing weight or experimenting with the way that food affects your mood and energy levels, keto may be worth a try (always consult your doctor before beginning any new diet plan). However, the average person can experience many of the positive effects associated with ketogenic diets — weight loss, sustained energy, and mood stability — by consuming a diet that is high in healthy fats, moderate in complex carbohydrates, and plentiful in a variety of fruits and vegetables.
References
Ebbeling, Cara B., et al. “Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial.” Bmj 363 (2018): k4583.
Gibson, Alice A., et al. “Do ketogenic diets really suppress appetite? A systematic review and meta‐analysis.” Obesity Reviews 16.1 (2015): 64-76.
Hu, Tian, et al. “Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials.” American journal of epidemiology 176.suppl_7 (2012): S44-S54.
Leibel, Rudolph L., Michael Rosenbaum, and Jules Hirsch. “Changes in energy expenditure resulting from altered body weight.” New England Journal of Medicine 332.10 (1995): 621-628.
MacLean, Paul S., et al. “Biology’s response to dieting: the impetus for weight regain.” American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 301.3 (2011): R581-R600.
Paoli, Antonio. “Ketogenic diet for obesity: friend or foe?.” International journal of environmental research and public health 11.2 (2014): 2092-2107.
Schwingshackl, Lukas, and Georg Hoffmann. “Comparison of effects of long-term low-fat vs high-fat diets on blood lipid levels in overweight or obese patients: a systematic review and meta-analysis.” Journal of the Academy of Nutrition and Dietetics 113.12 (2013): 1640-1661.