Keto is without a doubt the fad diet of the decade. Recipes for keto-friendly meals keep popping up on your social media feeds, your aunt actually lost weight on it and your colleague keeps updating you about his state of ketosis. So is it time for you to seriously consider keto?

If high-fat foods like bacon, cheese and nut butters* are the foods you tend to crave, and if never getting to eat breads, sweets and other carby stuff is something you think you can handle, keto can certainly sound like a tempting way to lose weight. But, it’s important to understand that no matter what its devotees tell you, keto is not an easy diet to follow, at least not on a long-term basis. Before you overhaul your entire diet and lifestyle in the name of keto, take the time to thoroughly research its pros and cons and the reality of eating according to its rules. And of course, consult your physician or a registered dietitian first.

*Spoiler alert: peanut butter is actually not allowed on keto.

What is Keto?

The keto diet was originally created almost a century ago as a treatment for childhood epilepsy, and it is proven to be effective in this function. Keto as a weight loss diet is a much more recent fad, although it does have similarities with other low-carb diets popular since the 1970s, such as Atkins and the South Beach Diet.

Keto focuses on the ratios of macronutrients – fats, proteins and carbohydrates – in the diet. Exact recommendations vary, but a typical keto diet proscribes getting just 5 to 10 percent of your daily calories from carbohydrates, which usually translates to 50 grams or less per day. Keto requires 10 to 20 percent of your daily calories to come from proteins, leaving the remaining 70 to 80 percent for fats.

A diet that matches the required ratios of macronutrients for keto looks quite different from the typical western diet.

The following foods are not allowed on keto:

  • Beans and legumes, including peanuts
  • Whole and refined grains, including breads, pasta, rice, cereals and baked goods
  • Starchy vegetables e.g. potatoes, corn, carrots, sweet potatoes
  • All fruits except for small amounts of berries
  • All fruit juices
  • Most alcoholic drinks
  • Most condiments and sauces
  • All sugary foods
  • Milk and most dairy products

These are some of the foods that can make up the volume of your diet on keto:

  • Fatty cuts of meat and processed meats
  • Butter and oils
  • Seeds and certain nuts
  • Oily fish
  • Avocados
  • Eggs
  • Hard cheeses
  • Olives
  • Non-starchy vegetables e.g. leafy greens, cruciferous vegetables, onions, mushrooms, summer squashes, asparagus and tomatoes.

How Does Keto Work?

The body typically uses carbohydrates (in the form of glucose) as its primary energy source. In the absence of glucose, the body will instead switch its energy source to ketones, a form of energy produced from stored fats. By cutting almost all carbohydrates from the diet and replacing them with fats, keto forces the body into a state of ketosis, meaning it burns fats (in the form of ketones) for energy instead of glucose. The state of ketosis ends as soon as you start eating carbohydrates again.

Further, because the keto diet is so high in fat and fat is very satiating, those following the diet tend to feel full while consuming fewer calories overall compared to a typical diet. This reduction in overall calorie consumption amplifies weight loss and reduces hunger and food cravings.

What are the Effects of Keto?

Aside from the permission to eat lots of fatty foods, which are generally off-limits on typical weight-loss diets, the major draw of keto is its promise of dramatic weight loss results in a relatively short period of time. When it’s followed properly, keto can demonstrate significant weight loss results in the short term. Both anecdotal evidence and scientific studies show this to be true.

A Harvard School of Public Health review of available studies concluded that the keto diet, followed properly, results in significant short-term weight loss, improved cholesterol and blood pressure levels and a reduction in hunger and cravings.

However, the same review explained that these benefits do not continue on a long term basis. Over time, the weight loss results from a keto diet are no greater than those on typical weight-loss diets. There is also a shortage of long-term studies of the keto diet, most likely because it is difficult to maintain on an ongoing basis.

Anyone considering keto should also know about its often-reported side effects. These include:

  • The “keto flu.” For up to a few weeks after beginning a keto diet, followers report symptoms including headaches, low energy and “brain fog.” These symptoms do disappear in time.
  • Constipation due to the lack of fiber inherent in a keto diet
  • Increased urination as a side effect of ketosis. Not only is this inconvenient, but it can also cause a loss of electrolytes (e.g. sodium, magnesium, potassium) that can ultimately be damaging to the heart. Another hazard is dehydration, which can damage the kidneys
  • Muscle loss. Muscles, including the heart, require carbohydrates for maintenance.

Considerations: The Pros and Cons

Understanding the dramatic dietary overhaul required to follow the keto diet is the first step for anyone considering it. The next step is to delve more deeply into the pros and cons of the diet. Consider the following:

Nutritional Balance

Nutritional balance is probably the most important consideration when it comes to understanding the pros and cons of keto – a diet founded on deliberately creating a heavy imbalance in your sources of nutrition.

Dietitians have long agreed that a healthy diet depends on eating a balance of proteins, fats and carbohydrates, something generally best achieved by embracing variety. USDA Dietary Guidelines for Americans recommend embracing a variety of nutrient-dense foods across all food groups, as well as limiting calories from saturated fats.

Keto goes against these guidelines in two ways. First, it eliminates entire food groups including starchy vegetables, beans, legumes, and most fruits, which are some of the healthiest, most nutrient-dense foods of all. Second, it dramatically increases the intake of fats, including saturated fats.

Proponents of keto argue that its requirements for macronutrients can be met while also getting all the essential micronutrients, such as vitamins, minerals, to be healthy. While this is arguably possible, generally with the assistance of a registered dietitian in strict meal planning, it is difficult. Writing for Harvard Health Publishing, Marcelo Campos, MD warns that those following keto tend to rely on unhealthy foods, such as processed foods and meats high in saturated fats, to meet its requirements for fat intake.

In short, eliminating entire food groups and eating large amounts of saturated fats goes against long-standing recommendations to eat a nutritionally balanced diet.


Keto is a rigid diet with a lot of rules and very little flexibility. By cutting out many major food groups, including fruits, starchy vegetables, grains, beans, and legumes, it dramatically reduces the variety of foods available to its followers. Getting the macronutrient balance right requires strict meal planning with little room for spontaneity. For some people this makes it easier to follow than a more flexible diet; for others, it makes it impossible to maintain in the long term.

Relying on putting the body into ketosis for its weight loss results means that the keto diet works only as long as it is followed to the letter. Reintroducing carbohydrates to the body puts an immediate end to the state of ketosis, and therefore to the weight loss effects of the diet.

Matters of Taste

The dramatic elimination of whole food groups required to follow a keto diet immediately rules it out for many people. Anyone who doesn’t enjoy eating fruits, baked goods, starchy vegetables (and don’t forget peanut butter), and can’t get enough butter, meat and ideally leafy greens will love keto meals. How many people do you know whose cravings match those descriptions?

Further, those who do crave high-fat foods might find a keto diet enjoyable at first, but in the long term find it difficult to maintain that enthusiasm. There are few long-term studies done on the keto diet simply because it becomes unenjoyable and therefore not maintainable. Of course, there are exceptions, but these are few.

Lifestyle Factors

Maintaining the keto diet while cooking for yourself is a challenge, but many people can handle that challenge. The keto diet is popular, so clearly many are able to follow its rules.

Eating out at restaurants, friends’ houses, work events, and parties pose an even greater challenge. Asking for substitutions and explaining your diet in order to keep following it outside your own house is something not everyone is comfortable doing, especially not on a long-term basis. Keto-followers can get around this by packing their own snacks and meals to eat outside the home, researching restaurants and menus in advance, and advising others about their diet. But these lifestyle changes are certainly not tenable for everyone.

Conclusion: Consult Your Physician

The keto diet is dramatic, inflexible and difficult to maintain in many ways. Additionally, its health benefits are debatable. If you have done diligent research, weighed the pros and cons and still feel like keto might be right for you, the final, essential step is to discuss it with your physician or registered dietitian, or preferably both.

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