The Truth About the Keto Diet

Blog Post

Stephen W. Farrell, PhD, FACSM
The Cooper Team
January 23, 2019

Here we go again… The internet is buzzing about the latest dietary fad, the Ketogenic Diet. Unlike other diet plans, the Ketogenic (or keto) Diet isn’t actually new. This low-carbohydrate diet is similar to the Atkins Diet of the 1970s and the South Beach Diet of the late 1990s. Same diet, different name.

The recommendation for the Ketogenic Diet is that you should consume only about 5-10% of your daily calories from carbohydrates, 70% of your calories from fats, and the remaining 20-25% from protein. By way of comparison, the dietary recommendations from the Institute of Medicine (IOM) are 45-65% of daily calories from carbohydrate, 20-35% from fat, and 10-35% from protein. The IOM recommendations are backed by groups like the American Heart Association, American Cancer Society, American Diabetes Association, the Surgeon General’s Office, and the overwhelming majority of Registered Dietitians.

To enter ketosis and meet the low carbohydrate goal of the Ketogenic Diet, one must significantly limit whole grains, dairy, fruit, some vegetables, and legumes (namely beans and peas). This leaves the dieter with the only options of eggs, butter, meat, fish, poultry, salad, nuts, seeds and oily salad dressings. Because dietary carbohydrate is extremely limited on the keto diet, the body cannot rely very much on carbohydrate as a fuel source for energy. This triggers a metabolic state called ketosis - a response by the liver to produce ketones, which are made from fatty acids. The ketones travel through the blood where they are used as a primary fuel source by the central nervous system (brain and spinal cord) and used to a lesser extent as fuel by other tissues. Ketosis will also result in the body’s use of protein (e.g. muscle) as fuel to some extent.  

The Ketogenic Diet has exploded in popularity recently because it does cause rapid, and sometimes dramatic weight loss. It’s not unusual for people to lose 8-12 pounds during the first couple of weeks. The internet is filled with testimonials from people who have supposedly stuck with it long enough to lose 50 lbs or more in just a few months. Combined with the perception of scientific validity, it’s no wonder why this is the latest fad. But take a closer look and you will see that it isn’t all it claims to be.

Three reasons why keto isn’t all it claims to be

First, if one is trying to lose weight, they should be striving to lose fat weight. The scale does not tell us what kind of weight we are losing. Our body is about 60% water by weight. Carbohydrate is stored in our body as a substance called glycogen, which is found mostly in muscle and liver cells. Each gram of glycogen we store is accompanied by two grams of water. When we restrict carbohydrate intake, glycogen levels are depleted, and we rapidly lose a lot of water weight via increased urination. This does not make us healthier, but it does make us somewhat dehydrated.  

Second, following the Ketogenic Diet means carefully tracking your macronutrients (protein, fats, carbs, and water), in addition to some micronutrients like vitamins and minerals. It can be an arduous task that makes simple calorie counting seem like a breeze. While most proponents of keto tout that calorie counting isn’t the main focus, the fact is that most people on this plan are also restricting calories. Any diet that creates a calorie deficit is likely to induce weight loss. While this makes it somewhat difficult to determine if the weight loss is the result of calorie restriction or from being in ketosis, The Cooper Institute’s position is that it is the former, not the latter.  

Third, there is a lack of long-term scientific data to support this diet. Most diet studies (as well as testimonials) are short-term, lasting only weeks or months. The short-term studies on Ketogenic diets have shown short-term weight loss as well as temporary improvements in important risk factors like HDL and LDL cholesterol levels, blood glucose, inflammatory markers, and waist circumference. However, any dietary approach that leads to weight loss will tend to show these same types of improvements.  To date, there are no significant studies to show that the Ketogenic diet leads to long-term weight control or improved health. In fact, some of the latest research suggests that it may be harmful in the long run.

Keto Cons

For most people, the perceived ‘pros’ of the Ketogenic Diet are outweighed by the following ‘cons.’

  • Lack of variety. So many foods are limited with this approach that you will likely soon tire of eating the same things over and over again.
  • Lack of fiber. Complex carbohydrates are the only source of dietary fiber! Since carbohydrate intake is very limited with the Ketogenic diet, you will be consuming a very low fiber diet by default. Low fiber diets are strongly associated with an increased risk of constipation, hemorrhoids, type 2 diabetes, cardiovascular disease, and digestive cancers. Think about that for a moment (or two).
  • Lack of essential nutrients. Ketogenic diets are notoriously low in several essential nutrients including vitamins C and D, as well as some of the B vitamins. Calcium is also lacking. Most Ketogenic diet enthusiasts remain unaware that complex carbohydrates contain hundreds of beneficial substances called phytochemicals; which are naturally occurring non-nutrients that help to prevent disease.
  • Not a long-term solution. The weight loss from the Ketogenic approach is typically temporary, not permanent. When you change your eating habits short-term, your weight will also change short-term. The goal should not be short-term weight loss, but rather, long-term weight control.
  • Fatigue and irritability. A Ketogenic diet increases the likelihood of hypoglycemia (low blood glucose levels) and can trigger what is known as the keto-flu. Symptoms may include headaches, fatigue, irritability and more unpleasant symptoms.
  • Inability to perform regular sustained exercise. Carbohydrate is a major fuel source for muscles during exercise. When carbohydrate stores are low and/or hypoglycemia is present, it’s very difficult to exercise. Diet plus regular exercise is far more effective for long-term weight control than either one by itself.  

We gladly acknowledge that ketogenic diets have been shown to be helpful in treating severe epilepsy, and that a few people will be able to sustain their weight loss using this approach. Even for those dedicated few, long-term weight control will mean cycling in and out of ketosis. Unfortunately, more and more studies suggest that low-carb diets may actually increase your risk  for all-cause mortality, as well as cardiovascular disease and cancer mortality. For the majority of the population though, the strict macro tracking, dietary limitations, and unpleasant side effects are enough reason to drop this fad and aim for making healthier lifestyle changes.


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