This post is part of the “To Try or Not to Try” blog series. Written by a registered dietitian (RD) or dietetic intern, each post explores the claims and science surrounding a different dietary pattern or trend. After compiling this research, each RD or RD2be gave the diet a grade based on whether it appears to hold up to the hype. A = “yes, go for it!” and F = “no way, absolutely not!”
About the Author:
Laura Casterline is a Registered Dietitian Nutritionist (RDN) based in Bedford, New Hampshire. She works as a private-practice dietitian under Nutrition in Motion, LLC, where she focuses on weight management counseling, corporate wellness, and sports nutrition. When Laura isn’t helping others reach their goals, she is out pursuing her own personal goals of staying physically active, strong, and adventurous. Stay connected with Laura on Instagram: @laurac_fit_Rd
What is it recommended for?
The ketogenic diet is recommended on mainstream platforms for weight loss (primarily fat loss) as well as for blood glucose regulation among diabetic individuals. Within the medical community, the ketogenic diet is known as a drug-free alternative treatment for patients (primarily children) that suffer from epilepsy (chronic seizures). The ketogenic diet has also been used for drug-resistant Glucose Transporter 1 Deficiency Syndrome (GLUT1DS), which is a genetic metabolism disorder with seizures as the most common symptom. Due to the neuroprotective effects observed from ketosis, researchers are currently considering the possible benefits for other brain disorders such as Parkinson’s, Alzheimer’s, Autism, multiple sclerosis, and even brain cancer. 1
What foods are allowed?
The ketogenic diet is very restrictive, which is why it is difficult to follow long-term. Foods that are high in fat and low in carbohydrate are considered ideal. Unfortunately, individuals that follow this diet do not always consume fat from the healthiest sources.
High-fat foods that are encouraged include:
- Red-meats (Bacon, Hamburger, Steak, Roast Beef)
- Processed high-fat deli meats (Salami, Pepperoni, Bologna)
- Fatty Fish (Salmon, Tuna)
- Oils (Canola, Coconut, Peanut, Olive, Vegetable, Sunflower, etc.)
- Full-fat dairy products (Cheese, butter, whole milk)
- Nuts & Nut Butters
Carbohydrate foods that are extremely limited include:
- All fruits
- All veggies (both starchy and non-starchy)
- Whole grains (oats, quinoa, brown rice, whole grain bread, etc.)
- White bread
- Added sugar (including but not limited to honey, maple syrup, agave, corn syrup, sucrose (table sugar), fructose, maltodextrin, dextrose, invert sugar, etc.)
What is the overall nutrient profile?
Most individuals that follow the ketogenic diet consume 5-10% of their daily calorie needs from carbohydrates (generally a daily max of 30 grams), 15-30% from protein, and 60-75% from fat.
Are the claims supported by science?
There is solid evidence to support that the ketogenic diet reduces seizures in children. 1 Additionally, there are some pilot studies that have shown that the ketogenic diet is beneficial for patients with brain tumors, specifically glioblastoma multiforme. 2 However, more research needs to be done on this topic before the ketogenic diet is prescribed as a treatment for brain tumors or brain cancer.
A large amount of controversial information currently exists on the effects of the ketogenic diet on weight loss, blood glucose control, and cholesterol numbers. Studies have shown that the ketogenic diet (with low-moderate saturated fat intake) can improve fasting blood glucose levels and insulin resistance in both diabetic and non-diabetic patients when measured short-term. 5 The effects that the ketogenic diet has on cholesterol levels depends directly on the breakdown of the types of fat consumed (unsaturated vs saturated). Among obese individuals, cholesterol values are negatively affected when consuming a high-fat, low-carb diet consisting mostly of processed high saturated fat foods. Meanwhile, studies have shown that when obese subjects followed a ketogenic diet high in unsaturated fats and low in saturated fats, both HDL levels and the size of LDL cholesterol increased. 6 It is important to note, however, that there is no long-term research currently analyzing the ketogenic diet’s effects over time on diabetes and cholesterol. Additionally, these findings were observed in obese subjects and thus may not appear the same in lean individuals.
When it comes to weight loss, there are several studies that show the benefit of using the ketogenic diet short-term. Previous research has shown good evidence of faster weight loss using the ketogenic diet when compared to those following a low-fat diet or even Mediterranean diet.1 However, there is no evidence that the subjects were able to keep the weight off. A 2016 study found that obese subjects that followed 4 weeks of a high-carbohydrate diet, followed by 4 weeks of the ketogenic diet lost more fat during the first 4 weeks than in the last 4. During the ketogenic diet, the participants lost more water weight, which made it look like they lost more weight overall. However, the loss of body fat (1/2 lb. lost) was comparable to that of a high-carb diet (1 lb. lost). There have been no significant studies done on the effects of using the ketogenic diet for weight loss long-term. 1
There have not yet been any studies done on humans focusing on the effects of a high-fat, low-carb diet on the gut microbiome; however, there are studies on mice and other small mammals. These studies found that the gut flora is negatively affected when carbohydrates are restricted. 4
This outcome may be because when carbohydrates are restricted, that means that dietary fiber (what the gut flora needs to remain healthy) is also being restricted. It is possible to follow a ketogenic diet and keep your gut microbiome “close to normal” by eating very fiber-rich low-carb foods such as artichokes, onions, and garlic. However, it isn’t very realistic to expect most individuals to try to incorporate these foods into their everyday eating regimen.
Are there any possible hormonal disturbances?
The main regulatory hormone that is affected by the ketogenic diet is insulin. As stated above, studies show that there may be a benefit to using the ketogenic diet short term to regulate glucose and insulin levels.
Another topic that is of concern is whether a low-carb diet has detrimental effects on women’s hormones. Studies suggest that a low-carb diet can put stress on a women’s HPA axis (hormones regulated by the hypothalamus, pituitary, and adrenals). 7 Some evidence also suggests that the ketogenic diet can cause an elevation of cortisol (the stress hormone) which will escalate any other imbalances of hormones within the body. If someone has pre-existing hormonal imbalances, they should talk to their doctor before trying the ketogenic diet.
Who should definitely not try this diet?
- People taking certain medications: Individuals on medications should not go on the ketogenic diet without consulting with their doctor first. The diet can alter blood pressure, glucose levels, etc., and thus their medications may need to be adjusted. 3
- People with diabetes: Individuals with diabetes should never switch to the ketogenic diet without medical supervision. Blood glucose lowering medications, insulin, etc. would need to be adjusted to avoid running the risk of metabolic acidosis.
- Heart disease: Those who have heart disease generally need to follow a low-fat, low-sodium diet. Most foods consumed on the ketogenic diet are processed high-fat, high-sodium foods.
- Kidney disease: Individuals with kidney disease or kidney failure should not go on the ketogenic diet. A high-fat, high-protein diet puts extra stress on the kidneys and can potentially worsen or progress the disease.
- Children: Growing children need an adequate balance of carbohydrates, fats, and proteins. They also need micronutrients, which are primarily found in carbohydrate-containing foods such as fruits and vegetables. The ketogenic diet generally recommends eating less than 30-50 grams of carbs per day to reach ketosis. There is no way that a child would be able to get their recommended daily intake of vitamins and minerals with this restriction.
- Post-cholecystectomy: Individuals that have had a cholecystectomy should be cautious when considering the ketogenic diet. The gallbladder contains bile that helps breakdown fats. Without the gallbladder, it is possible for the body to adequately breakdown a moderate amount of fat. However, if the body isn’t adjusted to consuming such large amounts of fat, the ketogenic diet may cause some digestive issues. These individuals should consult with their doctor or dietitian if considering the ketogenic diet.
- Pregnant and Breastfeeding Women: Prolonged maternal ketosis can be detrimental to the development of a baby’s brain and increase the risk for neural tube defects. There has not been any research on the effects of the ketogenic diet during breastfeeding on babies; however, we do know that during breastfeeding, the mother needs a balance of fat, protein, carbohydrates, and micronutrients in their diet. Doctors and dietitians do not recommend pregnant or breastfeeding women to follow the ketogenic diet.
- Athletes: There have been some studies to support the benefit of athletes using the ketogenic diet for performance improvement. However, none of these studies have been done long-term to see the effects on the body over time. We know that both strength and especially endurance athlete’s bodies prefer carbohydrates as their main fuel source. Athletes should speak to a sports dietitian prior to trying the ketogenic diet for performance.
Is this diet realistic and sustainable?
The ketogenic diet is realistic for short-term use when trying to reach a specific goal after consulting with their MD and/or dietitian. It is not realistic or sustainable for someone trying to lose weight and keep it off long-term. There is not enough research to show if there are detrimental effects on the body if a low-carbohydrate diet is followed for long periods of time.
What are the overall pros and cons?
The ketogenic diet can be beneficial to those using it for medical purposes or to reach specific short-term goals (such as glucose control) under medical supervision. However, from the perspective of a dietitian, any diet that restricts being able to eat the daily recommended servings of fruits and vegetables isn’t a good diet, especially long-term. From personal experience, I know that the ketogenic diet also has the potential to negatively impact resting metabolism (RMR) if used over a long period of time.
Forcing the body to essentially switch into “survival mode” by burning ketones for energy must put some stress on the body, which explains why the ketogenic diet has potential to raise cortisol levels in some individuals. I personally believe that a better approach to fat loss is to talk with an RD about adjusting macronutrients, exercise, and eating nutritious foods to fuel your body and lose weight in a healthy way that will last.
Additionally, those who follow the ketogenic diet may be at risk for micronutrient deficiencies, especially if they do not take a multi-vitamin supplement. The ketogenic diet restricts many nutrient-dense foods. Possible deficiencies could be of micronutrients found in fruits, veggies, and whole grains such as vitamin C, vitamin A, thiamin, riboflavin, niacin, folic acid, etc. Due to the fact that individuals on the ketogenic diet lose water weight, there is also a risk of developing deficiencies of potassium, sodium, and magnesium.
What grade do you give this diet?
I would give the diet a C. It is a useful tool for certain medical conditions, as well as for improving glucose control for some diabetic individuals. However, for sustainable fat and weight loss, I do not believe this diet to be the best strategy. The ketogenic diet has truly become a fad diet and appears to be the latest weight loss trend marketed through the media. Many people are trying the diet without first consulting with their doctor or a dietitian, which can be potentially dangerous to their overall health.
What is your general recommendation for a healthy eating pattern for the average human?
I believe that the average human benefits from a well-balanced diet consisting of nutrient-rich carbohydrates, fats, and proteins. Each meal should be colorful, with at least half of the plate composed of veggies and fruits. There should be no restrictions, but rather a focus on eating primarily whole foods, with some flexibility for those other foods you love in moderation 😊
Meet with an RD to discuss your needs and goals this upcoming year!
This content is intended for informational and educational purposes only. It is not intended as medical advice, medical nutrition therapy, or individualized nutrition counseling. Talk to your doctor or another licensed healthcare practitioner before making any changes to your diet, medications, or exercise routine. The opinions of these authors are their own and are not approved, sponsored, or endorsed by any professional organizations including but not limited to the Academy of Nutrition and Dietetics, United States Department of Agriculture, Food and Drug Administration, National Institutes of Health, American Heart Association, and American Diabetes Association.