The ketogenic diet is not new, but it seems that way on social media where celebrities and regular folk are touting its weight loss benefits left and right.  The premise is to reduce carbohydrate intake to 50g (or sometimes <20g) per day.  When carbohydrates are restricted to this amount, it takes a  few days the body’s glucose reserves become insufficient to produce energy for the central nervous system and brain. [1] [2] [3]  [4] [5] [6] The central nervous system needs an alternative energy source which comes from ketones produced in the liver from fat and amino acids.  Ketones are easily metabolized by various tissues, especially skeletal muscle, kidneys, and the heart.

What’s the big deal about using ketones as an energy source?  Our bodies shift to fat burning in order to provide the glucose necessary for some tissues.  Ketones also have an inhibitory effect on fat storage whereas glucose ingestion can trigger fat storage, and ketones provide fuel to certain parts of the body in the absence of glucose.  It sounds ideal right?  Many studies show that initial weight loss is greater on ketogenic diets than on low fat high carbohydrate diets. [7] [8]  Some of this initial weight loss in attributed to greater water loss on low carbohydrate diets, however.  Rapid weight loss of up to 10lbs in 2 weeks has been reported, and lean body mass is largely maintained compared with high carb diets where some muscle is lost too.

Are there adverse effects to the keto diet?  In general, the diet is considered to be safe, for a temporary period (up to 2 years).  The most common and relatively short-term side effects known as “keto flu” include symptoms such as nausea, vomiting, headache, fatigue, dizziness, insomnia, difficulty in exercise tolerance, and constipation.  These symptoms typically resolve in a few days to a few weeks. [9] [10] Reported long term effects can include fatty liver, hyperproteinemia, kidney stones, and vitamin and mineral deficiencies. [10]  Long term compliance with ketogenic diets are low, but some research has shown that moving from a ketogenic diet to a low carb (<45% carbohydrate) Mediterranean diet resulted in both long-term compliance as well as maintenance of reduced weight. [11]

In general, a Mediterranean style of keto is preferable.  Left to our own devices, it is tempting to eat less healthy fats such as bun-less bacon cheeseburgers than salmon, salad with olive oil vinaigrette and avocados.  The Mediterranean version ensures more nutrient dense foods and more fiber than a typical American version of keto.

Is ketosis the same thing as ketoacidosis?  No, ketosis is considered safe, whereas ketoacidosis is considered to be potentially life-threatening.  The difference is the amount of ketones as well as sugar in the bloodstream.  Here’s a table to help explain:

From <https://www.healthline.com/health/ketosis-vs-ketoacidosis#diagnosis>

Is ketosis safe? In general, the ketogenic diet in the short term (<2yrs) is considered safe, and effective, however not enough is known to determine its safety and efficacy in the long-term.  Switching to a lower carb but not keto diet high in fiber (make ½ your grains whole grains) and healthy fats may be less restrictive and easier to stick to.  While on keto, it’s important to monitor renal function which can be done at your doctor’s office or by using ketone urine tests.  People who have liver failure, pancreatitis, fat metabolism disorders, porphyria, or some other metabolic deficiencies should speak with their doctor before trying low carbohydrate diets.  In-season athletes should also be discouraged from very low carbohydrate diets, as the ability to perform at high intensities is severely reduced.  However, to help induce fat loss, trying keto early in pre-season may be beneficial if training volume is higher and doesn’t include high intensities. [12]

Is Keto better than other diets?  Compared with other diets, keto is better for quick weight loss, (some of which must be attributed to water loss.  Meta-analyses of comparable diets do not show conclusive evidence that keto is any better over time than a calorie restricted high carbohydrate diet. [13] [14] [15] [16]  Interestingly, a recent cohort study exploring over 25 years of associations between carbohydrate consumption and mortality, both low carbohydrate diets (where less than 40% of total calories came from vegetables, fruits and grains) and high carbohydrate diets (where more than 70% of total calories came from refined carbohydrates like sugars and white rice) were associated with increased mortality in people without diabetes.  Meanwhile, diets around 50-55% carbohydrate were associated with the lowest risk of mortality. [17]  Whole grains have been shown to be protective against heart disease.  An extra 2 servings per day of these foods has been shown to reduce risk of coronary heart disease by up to 20%.  (Conversely, 2 servings of sugar sweetened beverages per day have been shown to increase the risk of hear disease by as much.) [18]

Keto is not a great diet for athletes.  While it’s true that in ketosis, people can maintain steady state, low intensity exercise for as long or longer than those on high carb diets without depleting muscle glycogen, athletes have little to no energy for high intensity exercise.  It has been proposed to be a decent diet to try early in pre-season to help athletes perform prolonged easier steady state cardio and lose more fat mass, however multiple studies have shown a marked drop in ability to produce power.  Perceived exertion, heart rate and the amount of oxygen consumed are all greater on keto than on a mixed diet which suggests, that to perform the same activity, athletes on keto are actually working harder. [12] [19] [20]

When it comes to weight loss and dieting there are many ways to skin a cat.  If you think you want to try keto and your goal is to lose weight fast, be sure to eat plenty of high fiber fruits and vegetables while on keto.  Have at it for a short- term weight loss boost!  Plan easing yourself back onto carbs for a few weeks before heading to your next nutritional goal.

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