The ketogenic diet, or “keto” for short, has become one of the most popular diets for those looking to lose weight.  But does it really work, or is it just another fad? This article touches on the pros and cons and summarizes the latest research.

Unless everyone you know eats perfectly and has never tried a diet, chances are you know someone that has at least tried keto.  You may be asking yourself “well they lost weight and it seemed to work for them, so it probably works right?” Not necessarily. Remember you don’t always know the full story. Your friends and even family may outwardly talk about the positive and what things are going well in their life, rather than something that is not working well or going wrong.  It’s human nature to want to show off the good things and keep the “bad” things quiet because we’re not proud we “failed” at something or made a mistake.  I always think about those I know that gamble. They always share when they win money, but I never hear about the times they lost (and trust me – I know it’s happened!).

As a Registered Dietitian that promotes mindful eating and a balanced diet, I often help my clients to move away from restrictive fad diets. However, I know that they aren’t going anywhere anytime soon and many of you still have an interest and questions regarding these diets, so I thought it was only fair and appropriate to provide you with the facts.  Many of my clients come to me after trying keto or other types of popular diets, and so I always provide the evidence and the facts so that we can come to the best decision together on a healthy plan for them.  I make no money for providing you with this evidence so there is no other reason for me to present it to you other than to inform you of the facts.

Ok.  So what exactly is the ketogenic diet?

The keto diet is a very low carbohydrate (typically less than 50g/day and can be as low as 20g/day), moderate protein (10-15% of calories), and high fat diet (100-150g). (1) The basic premise of the keto diet is if you deprive your body of glucose (which comes from carbs in your diet) your body then begins to break down your fat stores for fuel.  If your carb intake is low enough and your protein intake is moderate (but not too much), your body will transition to a state of “ketogenesis” where it burns more calories from the breakdown of your food. (19)

The problem is that glucose is your brain’s #1 source of energy for its daily vital functions.  On a keto diet, you are not providing your brain with glucose and instead it uses ketones as its energy source.  Have you ever felt brain fog or lack of focus?  Chances are that was because your brain was deprived of glucose and it needed to be repleted. (2)

Also there are many variations to the diet and if you’re not being properly monitored by a professional, it is easy to lose muscle. If you’re not getting enough protein and especially if you’re active, your muscle protein will be broken down for energy and you will lose your muscle stores. (9) This decreases your metabolism and can lower your immune system.

With all this being said, it does require more energy for your body to break down proteins and fat on a ketogenic diet than breaking down carbs on a more traditional, higher carbohydrate diet. With this increase in calorie-burning power, many do lose weight on this diet, especially in the beginning.  Low carb diets naturally may decrease your hunger hormones, resulting in less cravings. (7,8) It is questionable if it’s the very high fat content or the production of ketones themselves that helps with the satiating factor of this diet, at least in the beginning.

What foods are allowed on Keto?

High fat – oils, butter, lard, avocado, coconut, some nuts and seeds, meat and poultry

Moderate Protein – grass-fed beef, free-range poultry, pork, bacon, wild-caught fish, organ meats, eggs, tofu, some nuts and seeds

Very Low Carb – 30-50gm/day – berries, limited amount of dairy

What foods are restricted or need to be avoided?

Essentially all starches – pasta, rice, bread, bagels

Starchy veggies like carrots, potatoes, and corn

Simple sugars and sweets – cookies, cakes, candy

Soda and sweetened beverages

Most fruits except berries


So unless you hate all of these foods and never eat them to begin with (which I wouldn’t recommend!), chances are keto will not be an easy diet for you to follow.

What can I expect if I’m starting a keto diet?

In the first 2 weeks on a keto diet, many experience what is called the “Keto flu” where they may develop fatigue, lightheadedness, nausea and headaches. This is the result of sodium and fluid rapidly exiting your body as a reaction to a very low carbohydrate diet. This large shift in your body’s metabolism can cause these unpleasant symptoms. (20)  

The most success is typically seen in the first 2 months – where if the person can get over the keto flu hump, they may feel satisfied and lose weight fairly quickly during this time. However, there are studies to show after that 2 month period, something changes.  The weight loss slows, hunger and cravings return with a vengeance (often more than prior to following keto) and it becomes more difficult to adhere to. This then creates that vicious diet-binge cycle.

Okay, so what’s the bottom line? Give me the research!

There are no long term human studies (more than 24 weeks) to date on the keto diet. (10) A few studies to date have shown success in those with diabetes achieving better blood sugar control, improving LDL cholesterol (the “bad” cholesterol) levels, and reduced levels of the hunger hormone ghrelin. (20)

The kicker is after about a 2 month period.  Also it is questionable how long this diet can realistically be followed long term.  Restriction can be done temporarily especially when there is more motivation in the beginning.  But what happens after weight loss slows is that it becomes more difficult to stay motivated. (20)There is also question the effect on cholesterol levels long term with the high fat content in the diet, being 80-90% of the diet as opposed to the USDA requirements of 30%.  This is a huge difference and is yet to be determined how safe such a high fat diet truly is.

Additionally, following this diet puts you at risk for nutritional deficiencies such as magnesium, B vitamins, and potassium. It also can cause constipation and digestive issues as it is limited in foods that are natural fiber sources like fruits, beans, and whole grains.

I would not recommend this diet to anyone with a history of an eating disorder or has any type of unhealthy relationship with food.  Since this diet restricts many foods and puts foods into categories of good and bad, it only increases the chances of disordered eating behaviors.  

I would also not recommend this diet to anyone who is pregnant, as there is no research on the safety of this during pregnancy. Also during pregnancy and especially if you have morning sickness, carbs and starchy foods often are much better tolerated and sometimes all you can keep down.  You also need a balanced diet with plenty of fruits and vegetables, many of which are restricted on the keto diet.

If you or someone you know is following keto or thinking about it – I encourage you to ask questions and don’t just take it for face value. Do the research and reach out to me.  It’s your body and your health and you should know how your diet is affecting you. I don’t judge or ever force you to follow a diet you’re not comfortable with. I meet you where you are and help you to find something that works for you while getting to the root of your eating struggles.  No matter what diet you are following now, you need to be able to determine your real goals, struggles, and motivators in order to get from where you are now to where you want to be.  

Cheers to finding the perfect diet (or what I like to say “non-diet”) for you!


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2. Brouns F. Overweight and diabetes prevention: is a low-carbohydrate — high-fat diet recommendable? Eur J Nutr. 2018;57(4):1301-1312. 

3. Tinsley GM, Willoughby DS. Fat-free mass changes during ketogenic diets and the potential role of resistance training. Int J Sport Nutr Exerc Metab. 2016;26(1):78-92.

4. Paoli A. Ketogenic diet for obesity: friend or foe? Int J Environ Res Public Health. 2014;11(2):2092-2107. 

5. Zilberter T and Zilberter Y. Ketogenic ratio determines metabolic effects of macronutrients and prevents interpretive bias. Front Nutr. 2018;5:75. 

6. Gomez-Arbelaez D, Bellido D, Castro AI, et al. Body composition changes after very-low-calorie ketogenic diet in obesity evaluated by 3 standardized methods. J Clin Endocrinol Metab. 2017;102(2):488-498. 

7. Cicero AF, Benelli M, Brancaleoni M, Dainelli G, Merlini D, Negri R. Middle and long-term impact of a very low-carbohydrate ketogenic diet on cardiometabolic factors: a multi-center, cross-sectional, clinical study. High Blood Press Cardiovasc Prev. 2015;22(4):389-394. 

8. Johnston CS, Tjonn SL, Swan PD, White A, Hutchins H, Sears B. Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets. Am J Clin Nutr. 2006;83(5):1055-1061. 

9. Paoli A, Bosco G, Camporesi EM, Mangar D. Ketosis, ketogenic diet and food intake control: a complex relationship. Front Psychol. 2015;2;6:27. 

10. Sumithran P, Prendergast LA, Delbridge E, et al. Ketosis and appetite-mediating nutrients and hormones after weight loss. Eur J Clin Nutr. 2013;67(7):759-764. 

11. Gibson AA, Seimon RV, Lee CM, et al. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obes Rev. 2015;16(1):64-76. 

12. Saslow LR, Daubenmier JJ, Moskowitz JT, et al. Twelve-month outcomes of a randomized trial of moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes. Nutr Diabetes. 2017;7(12):304. 

13. Kosinski C and Jornayvaz FR. Effects of ketogenic diets on cardiovascular risk factors: evidence from animal and human studies. Nutrients. 2017;9(5). 

14. Volek JS, Sharman MJ, Forsythe CE. Modification of lipoproteins by very low-carbohydrate diets. J Nutr. 2005;135-1339-1342.

15. Olson CA, Vuong HE, Yano JM, Liang QY, Nusbaum DJ, Hsiao EY. The gut microbiota mediates the anti-seizure effects of the ketogenic diet. Cell. 2018;174(2):497. 

16. Fuehrlein BS, Rutenberg MS, Silver JN et al. Differential metabolic effects of saturated versus polyunsaturated fats in ketogenic diets. J Clin Endocrinol Metab. 2004;89(4):1641-1645. 

17. Ullah W, Hamid M, Mohammad Ammar Abdullah H, Ur Rashid M, Inayat F. Another “D” in MUDPILES? A review of diet-associated nondiabetic ketoacidosis. J Investig Med High Impact Case Rep. 2018;6:2324709618796261. 

18. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: The DIETFITS Randomized Clinical Trial. JAMA. 2018;319(7):667-679. 

19. Keto diet. U.S. News & World Report

20. Dennet C. The Ketogenic Diet for Weight Loss. Today’s Dietitian. 2019. 21(1):26.

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