The Keto Diet for Weight Loss:
The “skinny” on eating fat
If you’ve set foot in a gym anytime in the past year or so, you’ve probably heard of the ketogenic diet. You probably know a few people who swear by it. “Keto” is all the rage. As a fitness professional, I am peppered with keto questions whenever someone wants to discuss weight loss. “Does it work?” “What do you think of it?” “Is it safe?” “How does it work?” “Ketones are key, right?” “The keto diet can cure cancer and diabetes, right?” While I do have my own opinions on answers to these questions, I do not think my opinions are always correct.
So, in this 3 part series of articles, I decided to dive into the science of the ketogenic diet. Over the next few weeks, we will look at how the keto diet effects weight loss, if it helps with performance, and the benefits it holds for health and wellness.
This is Part I and addresses how the keto diet effects weight loss. In this (hopefully informative) article, I will answer 3 main questions in regard to the ketogenic diet and its role in weight loss. They are:
- What is the keto diet?
- Does it work?
- Why does it work?
What is the keto diet?
The keto diet originated in 1921 as a treatment for epileptic children when researchers discovered that blocking glucose metabolism suppressed inflammatory genes in the brain. With found success, the ketogenic diet as a prescription for aiding in the control of epileptic occurrences grew in popularity into the early 1980’s, until the development of pharmaceutical drugs phased out the popularity of the diet (1). From there, there’s not much hubbub on the keto diet until a Dateline story in 1994 discussed the benefits of a keto diet for a young boy with epilepsy, for whom prescription drugs were not working. And then the keto fad took off and grew into what we know it as today. The keto diet is now anecdotally claimed to improve the body’s ability to use fat for fuel (decreased reliance on carbohydrates), improve weight loss through ketone formation, be a superior method of weight loss as it “just burns fat”, “cure” Type II Diabetes, improve cholesterol numbers, and increase high-density lipid (HDL) numbers (good fats). And that all sounds amazing.
A true ketogenic diet is comprised of 75% fat, 20% protein, and 5% or less carbohydrate (2). However, most mainstream ketogenic diets are just really low carbohydrate with an emphasis on fat consumption as the major portion of the diet. The basic idea of this diet is that we can change our bodies from favoring the metabolism of carbohydrates as our main fuel source to instead favoring fat oxidation as our primary energy resource, with ketones being the major fuel source.
Fat is an important but secondary energy source in the human body. Our bodies crave carbohydrates for energy and this is the primary fuel source that our physiology prefers – carbohydrates are key in energy metabolism. In the absence of adequate carbohydrate availability, like what would happen during starvation, at the end of an ultra-marathon, or several months into a low-carb diet, the body has to turn to an alternate source to maintain energy and keep our systems going. Without any dietary restrictions there is an ample supply of glucose which the body readily uses as a primary fuel (6).
However,when there is not enough carbohydrate present, the body must shift to using fat as the primary energy source. In this case, the body breaks down stored triglycerides, which are bountiful, even the leanest individual. Essentially, the keto diet causes a physiological response carbohydrate restriction that mimics starvation. Because the body has a limited ability to store or produce carbohydrates for energy during periods of starvation, it switches to ketogenesis (6, 7).
Ketogenesis results in the production of ketones, a product of fatty acid break down performed by the liver, in the absence of carbohydrates for fuel use. Three primary ketone bodies are produced; acetone, acetoacetate and β-hydroxybutyrate. Very small amounts of ketones are always present in the bloodstream. However, only during periods of extremely low carbohydrate intake is there significant ketone production. This build-up of ketones in the blood is commonly referred to as “ketosis.”
Hence, the ketogenic diet (5, 6, 7).
The main objective of the keto diet is to sufficiently deprive the body of carbohydrates to the point that the body reaches “nutritional ketosis,” and switches over to using mainly fat for fuel. This “switch over” point is not seamless and it takes time for individuals to become “keto adapted.” In fact, it can take several weeks to several months for “keto adaptation” to occur. The idea is that a body will have very little reliance on glucose for brain function or as a source of energy for exercise, regardless of intensity (6, 7).
So, in summary, the keto diet tells us that we can eat a diet that is predominantly fat and reap health benefits and cause our bodies to function almost completely off of fat. Bring me the ice cream! Sign. Me. Up.
Does it work?
Well… yes, technically. And no. Many studies on the ketogenic diet claim weight loss in their titles. Several studies have dug deeper into the effects of low-carbohydrate or ketogenic diets on weight loss. For example, a study published in the American Journal of Clinical Nutrition (8) compared one year of low-fat vs. low-carbohydrate diet in adults with abdominal obesity. Subjects were randomly assigned to diet groups. The only stipulation of the diets was that the same amount of calories and macronutrients were consumed each day in the respective diets. The researchers found that there was statistically significant weight loss in both groups BUT, there was no significant difference in the weight loss between the groups. This means that a low-carbohydrate diet was equally as effective for weight loss as a low-fat diet.
When you unpack the data from this study and others like it, the results do show statistically significant weight loss but they also show an insignificant change in body composition, aka fat loss. Wait, what? What are we losing then?
Unfortunately, most of the weight being lost is either total body water or lean body mass or, in layman’s terms, muscle. In studies conducted on resistance trained men and powerlifters/weightlifters, the resulting loss in body mass after adherence to a ketogenic diet was roughly around 2 kg. 2 kg is approximately the amount of water that your body will hold on to when it is not glycogen depleted (3, 4, 5). This insinuates that the weight lost as a result of being on a keto diet may just be due to the fact that the body is no longer holding on to water. This does not mean that no fat mass was lost in those studies, just that it was not statistically significant.
Other studies found that diets with decreased carbohydrate intake and increased fat intake did lead to increased fat oxidation (3), decreased triglycerides, and increased HDLs (2). However, in these studies there was a very high rate of dropout in the low-carbohydrate groups. This indicates that this type of diet is hard to adhere to, but near complete adherence is necessary for success. Research also says that after 2 years on the ketogenic diet, compared to other diets, the only difference was that the change in HDLs remained; there were no significant differences in body composition when compared to calorie restricted diets (2).
The data of these studies, along with many others, indicates that the keto diet is not a superior method of weight loss or “fat burning”, it’s just another method of weight loss that may work for some people.
Why does it work?
The answer? It has nothing to do with ketones. The amount of fat oxidation that is created through adherence to a ketogenic diet is not enough to yield sustainable weight loss by itself, so the measurement of ketones is not the key to success in changing your body composition with the keto diet. High levels of ketones simply indicate that your body does not have enough glucose to metabolize for energy and thus fat is being used which makes sense since you are no longer eating high amounts of carbohydrates (6).
So why does the keto diet technically work? Current research shows that the resulting weight loss of a keto diet is from appetite suppression yielding a caloric deficit (2, 5). A recent meta-analysis investigated the impact of the keto diet on appetite and gave us some good answers (9). The meta-analysis included 12 studies which investigated the effect of either a very low energy diet (<800 calories per day) or a ketogenic low-carbohydrate diet (carb consumption of <10% of energy or <50 g/day, but ad libitum consumption of total energy, protein and fat). The studies were anywhere from 4 to 12 weeks long and resulted in total weight loss between 5.0 and 12.5 kg. Nutritional ketosis was confirmed via blood samples in all 12 studies for both diet groups. Both groups reported decreases in appetite throughout the study. This is interesting because even the group that was consuming less than 800 calories a day still reported a decrease in appetite, which should not happen! Those subjects should have been really hungry. In addition to this, the groups participating in the ketogenic low-carbohydrate diets also lost weight and experienced reductions in appetite, even though they were allowed to eat as many calories as the wanted while following their macronutrient requirements. These results provide some support for the idea that nutritional ketosis may have an appetite suppressing effect (9).
Fat is a very satiating macronutrient, weighing in at 9 kcal/g. It does not take a lot of it to make you feel full. This means that, theoretically, you would not need to consume as many calories throughout the day. This is huge for a diet since a large complaint people have while losing weight is that they’re “always hungry.” Weight loss = calories in < calories out. It really is that simple!
That’s the “skinny” on the keto diet. Research shows that it can lead to a weight loss, reductions in bad fat, increases in good fat, and some changes in body composition. However, it also says that the same results can be garnered from other diets that focus on calorie restriction without restricting carbohydrates since the success of the keto diet likely comes from appetite suppression and definitely not from the mystical powers of ketone bodies.
“Okay, great, but what should I do?”
Well, if you’re someone who struggles with appetite suppression when dieting, the keto diet might just be worth a try. Just remember, for it to work for weight loss, you really need to stick with the appropriate macronutrient recommendations of the ketogenic diet. Or if you’re sick of eating brown rice, broccoli, and plain chicken all the time, the keto diet could give you something new to try. At the end of the day, calories are calories when it comes to weight loss.
No matter what, when you start a new diet make sure that it is the right thing for YOU. Is it realistic for you to stick to the restrictions? Is it safe for your health? How does your body respond to being in a low-carbohydrate state? If you’re unsure of it’s safety for your health, talk to your doctor or registered dietician. If you would like help planning and managing a ketogenic diet, please reach out to us at: email@example.com.
This article does not necessarily represent the views/opinions of MadLab Performance, LLC. This article is not meant to recommend health solutions in place of a doctor or other medical professional and should only be used to help those reading it gain more information prior to making their own decision.
Cayley is a strength coach and organizational fiend from North East, MD. Outside of work, she enjoys baking, training to become harder to kill, and being a wife and mom. Cayley works for Mad Lab Performance as Administrative Coordinator and may be contacted at: firstname.lastname@example.org
(1) Livingston S. Comprehensive Management of Epilepsy in Infancy, Childhood, and Adolescence. Charles C Thomas, Springfield, IL, 1972, pp. 378–405.
(2) NSCA Personal Trainers Conference 2019. The PaleoKetoVeganMacroFasting Diet: Stop the Madness, Baltimore, Maryland: Shawn M. Arent, PhD, CSCS,*D; 2019.
(3) Greene DA, Varley BJ, Hartwig TH, Chapman P, Rigney M. A Low-Carbohydrate Ketogenic Diet Reduces Body Mass Without Compromising Performance in Powerlifting and Olympic Weightlifting Athletes. Journal of Strength and Conditioning Research 2019;32:3373–81.
(4) Waldman HS, Krings BM, Basham SA, Smith JEW, Fountain BJ, Mcallister MJ. Effects of a 15-Day Low Carbohydrate, High-Fat Diet in Resistance-Trained Men. Journal of Strength and Conditioning Research 2018;32:3103–11.
(5) Willoughby D, Hewlings S, Kalman D. Body Composition Changes in Weight Loss: Strategies and Supplementation for Maintaining Lean Body Mass, a Brief Review. Nutrients 2018;10:1876. doi:10.3390/nu10121876.
(6) III CRG, Cscs. Low-Carbohydrate Ketogenic Diet for Weight Management. National Strength and Conditioning Association (NSCA) 2018. https://www.nsca.com/education/articles/ptq/low-carbohydrate-ketogenic-diet-for-weight-management/ (accessed June 15, 2019).
(7) Dhillon KK, Gupta S. Biochemistry, Ketogenesis. [Updated 2019 Apr 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.
(8) Brinkworth GD, Noakes M, Buckley JD, Keogh JB, and Clifton PM. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo. American Journal of Clinical Nutrition 90(1): 23-32, 2009.
(9) Gibson AA, Seimon RV, Lee MY, Ayre J, Franklin J, Markovic TP, Caterson ID, and Sainsbury A. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obesity Reviews 16(1): 64-76, 2015.