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September 21, 2018

Pitfalls of the lifestyle ketogenic diet

By Jennifer Fabe, registered dietitian

The therapeutic ketogenic diet has been used as a treatment for epilepsy for nearly a century. In recent years, we’ve learned even more about its potential role in treating other medical disorders. But lately, the lifestyle ketogenic diet has been getting a lot of attention for the wrong reasons. It has become a popular weight loss trend, and many people are jumping on the bandwagon without considering potential risks.

How does the ketogenic diet work?

In a typical diet, more energy comes from carbohydrates than from protein and fat. The reverse is usually true in a ketogenic diet, which is higher in fat and lower in carbohydrates.

Fortunately, our bodies can use two sources of fuel for energy—glucose, which comes from carbohydrates like bread, fruit, and rice, and ketones, which come from fats like butter, cheese, and oil. Because we typically eat more carbohydrates, our bodies use glucose as their primary fuel since it is easy to access. When there isn’t enough glucose available, our bodies will switch over and start using ketones for energy.

The therapeutic ketogenic diet is medically supervised. It intentionally deprives the body of glucose, which helps trigger a switchover to a state called ketosis. The diet prescribes fat rich food choices, often in very precise amounts. With limited access to carbohydrates and increased access to fat, the body adapts to using ketones as its primary fuel. We don’t know precisely how it works, but ketones seem to help stop or reduce seizures in many people who follow this diet strictly.

Therapeutic ketogenic diet versus lifestyle ketogenic diet

The therapeutic ketogenic diet is used to control seizures and other conditions, and is done under strict medical supervision. Just because it’s considered a “natural” therapy, doesn’t mean it doesn’t have risks. A therapeutic ketogenic diet:

• is customized for each patient, and only used when people meet certain medical criteria.
• is ideally started slowly over a period of weeks under close supervision to minimize side effects. Rapid initiation over a period of days is only done if absolutely necessary, and after serious medical consideration.
• may require a review, and/or adjustment of medications so they don’t magnify potential side effects.
• requires a commitment to daily consistency.
• is monitored regularly for effectiveness, tolerance, and side effects at home and by a medical team.
• is supplemented by vitamins and minerals needed for complete nutrition.

When people embark on a lifestyle ketogenic diet with the goal of losing weight, they often fail to consider the potential risks involved, and rarely get the medical monitoring that should accompany this diet. When it’s not being used for medical purposes, keto dieters are also more likely to “cheat.” And because it is so limiting, many people find it difficult to stay on the diet long term and maintain their weight loss.

Other potential risks

Starting the ketogenic diet without input from healthcare professionals can lead to negative effects. On websites promoting the keto diet, you may read that these side effects are normal and will go away if you persist on the diet. They are not normal, and shouldn’t occur if you are following the diet safely.

Keto “flu”?

Some people who follow a lifestyle ketogenic diet report feeling flu- like symptoms when they start, including headache, tiredness, nausea and aching. This should not happen. It is the body’s way of responding to rapid adjustment, but is unnecessary if the diet is introduced properly and under medical supervision.

Vitamin and mineral deficiencies

Fruits and vegetables, grains, and protein are important sources of vitamins and minerals in our diet. The keto diet restricts many of these foods. Without them, it’s hard to get the vitamins and minerals we need. A lack of certain vitamins and minerals can cause complications. For example, lack of selenium, a mineral that’s found in grains and some sources of protein, can cause an irregular heart rhythm.

Lack of minerals can also cause cramps, which are common when people start the keto diet without supervision. If not properly monitored, the diet can pose a risk over time for bone weakness, and can result in compromised growth in children.

a blood sugar monitor and a bottle of vitamins

Interference with medication

The ketogenic diet can also interfere with some medications, which is why patients are carefully screened before being put on this diet to control conditions like epilepsy.
The diet can interfere with some diabetes medications, causing the body to pee out too much sugar. This loss of sugar can drop blood sugars to a dangerously low level.


In a practical sense, the lifestyle ketogenic diet can add expense to your grocery list. Although you may buy less carbohydrate rich foods, purchasing high fat foods can be pricey.

Advanced Planning

Planning your groceries and meals is a great strategy for staying on track with healthy eating. The lifestyle ketogenic diet requires careful advanced planning to make sure you get the nutrients you need, and aren’t left scrambling for something to eat. Before dining at a restaurant, or accepting a friend’s dinner invitation, you should consider what you are going to eat. It’s also important to carry snacks you are able to eat on the go in case you get hungry.

But I’m losing weight on the ketogenic diet…

The ketogenic diet is a nutritionally extreme option for weight loss when implemented in its strictest form. Most lifestyle ketogenic diets, however, are less restrictive in carbohydrates than their medical counterparts and more liberal in fats. Although small amounts of ketones can sometimes be generated from this ratio of foods, it is likely not the reason for the weight loss. While some people may find it effective for this purpose, it doesn’t generally work well long-term.

Why do people lose weight then? Weight loss works on a very basic principle: calories burned exceed calories consumed. Whenever our bodies don’t get enough calories in the food we eat, they start to use other calorie sources within the body, like body fat or muscle. People who lose weight on the ketogenic diet are losing weight because they are consuming fewer calories than they are burning.

There are a few reasons for this:
• Fats tend to fill you up, so you don’t eat as much on the ketogenic diet.
• Some lower carbohydrate foods in the diet, like leafy greens, are very low in calories.
• The diet requires you to modify foods so they fit within its boundaries, which makes eating on the run difficult—therefore dieters eat fewer calories from takeout, fast food, and junk food.

Ultimately, this calorie imbalance causes weight loss, but it is difficult to maintain.

Because it restricts many important food groups, the ketogenic diet can’t provide complete nutrition without added vitamin and mineral supplements. Restrictive diets also tend to make us want what we can’t have. If we can’t have bread on a diet, we may crave it. When we give into those cravings, our body goes back to using glucose for fuel and the ketogenic diet is no longer maintained.

If you are still interested in trying the ketogenic diet, or are on the diet and want to continue, I strongly urge you to talk to your family doctor or a registered dietitian about how to follow the diet safely and sustainably.

Healthier alternatives

The best way to lose weight is by making healthy lifestyle changes you can stick with in the long run. There is no weight loss diet that ‘fits all’ for our diverse Canadian population. I recommend making healthy food choices that suit your preferences, food availability, and budget.

To work towards your weight loss goal and healthy lifestyle:

• continue to eat a variety of foods from all food groups in moderation, and make healthier choices within those food groups.
• commit time to planning your groceries, meals, and physical activity.
• be mindful of your portion sizes.
• talk to your doctor or registered dietitian for strategies and support to help you achieve your weight loss goals.

Here are some helpful resources on selecting healthy foods and appropriate serving sizes:

Jennifer Fabe is a registered dietitian in the Division of Pediatric Neurology at McMaster Children’s Hospital. She is the lead dietitian for the hospital’s ketogenic diet program, which helps kids with epilepsy use the medically supervised ketogenic diet to manage their seizures.