Ketogenic Diet Basics: How It Works and What to Do When It Doesn't

Interested in going, Keto? A registered dietitian & certified diabetes educator explains the pros, the cons, and the reasons why it might not be right for you.


black lab licking lipsFollowing a ketogenic diet isn't easy—truly putting your body into ketosis requires diligence, frequent blood sugar testing and measuring food in exact amounts. (Photo: Unsplash, James Barker)

Ketogenic Diet Basics 

The keto diet is so wildly popular—everyone knows someone who's tried it. But what is the keto diet exactly and is it the best diet for managing diabetes? Only you and your doctor can answer that, as individual considerations are an important component of weight loss success.To help get the conversation started with your doctor, you first need to know these keto diet basics.

What Is the Keto Diet & Why Is it Controversial?

The keto (technically ketogenic) diet is a very low-carb, moderate-protein, high-fat diet. Eating this way can be very restrictive, but the main advantage is that it shifts your body’s metabolism to using fat for fuel rather than carbohydrate.

The recommended dietary allowance for carbohydrate is 130 grams per day for people without diabetes, which is based on the brain’s requirement for glucose. However, the body is able to use alternate metabolic processes to provide this energy, even while eating very few carbohydrates1 When fat is used for energy, ketone bodies (also called ketones) are produced. Ketones can fuel the brain instead of glucose (a type of carbohydrate)—without increasing blood sugar and insulin levels.

This sounds ideal for the management of diabetes, but the keto diet is very controversial among health professionals. Mainly this has to do with the fact that the keto diet was originally used (as a last resort and often temporarily) for the management of seizures due to epilepsy.

Fortunately, because many people following a keto diet lose weight and have good results in terms of managing their  blood sugar, more research is being conducted in this area. However, because there is a lack of conclusive, long-term evidence, the ketogenic diet is often not recommended by physicians and registered dietitians for people with diabetes. And rightfully so. Weight loss is complex and there are definitely people with diabetes who should absolutely not be following a keto diet.

Who Should NOT Follow a Keto Diet?

According to the American Diabetes Association’s Standards of Care, a keto diet is not recommended for:

  • Women who are pregnant or lactating
  • People with or at risk for disordered eating
  • People who have renal disease2

The following people should use extreme caution when following a ketogenic diet:

  • People taking sodium–glucose cotransporter 2 (SGLT2) inhibitors due to the potential risk of ketoacidosis2
  • People with type 1 diabetes due to risk of hypoglycemia and diabetic ketoacidosis (a life-threatening hyperglycemic condition that results when there is a lack of insulin). Although recent research is showing promising results.3

(*Please Note: This article is not intended to replace medical advice. These are general guidelines. Always consult your own doctor for personalized medical advice.)

Pros of a Keto Diet

If you and your doctor decide a keto diet is right for you, the benefits may include:

  • Weight loss. Some research suggests a ketogenic diet may be more beneficial than other conventional methods for weight loss in people with diabetes. It appears to help people decrease or get off medications for diabetes as well.4,5
  • Improved blood sugar control. Because the majority of calories come from fat, rather than carbohydrates or protein, both of which raise blood sugar, blood sugar is often better controlled.4,5,6,7
  • Improved insulin resistance. A keto diet decreases glucose by limiting carbohydrate intake, which results in lower insulin levels, and as a result research suggests the keto diet results in dramatically-improved insulin sensitivity.7 At least one animal study links the amount of time on a keto diet to an increase in insulin resistance, so this requires more research.8
  • Appetite supression.After adaptation to the keto diet, feelings of hunger subside, which helps with sustainability and contributes to weight loss.9

Cons of a Keto Diet

On the other hand, following a keto diet has some potential risks, including the following:

  • It's a highly restrictive way of eating. Any highly restrictive diet may not be achievable or sustainable and extreme restriction can lead to eating disorders in those who are predisposed.
  • It may lead to yo-yo dieting with a return to the previous way of eating. A followup study of participants in the television program The Biggest Loser shows dieting and rebounding (decreasing and increasing body weight repeatedly) over a lifetime appears to negatively affect your metabolism.10
  • It's difficult as it requires an intense focus on food and calculations for each meal. Carbohydrates quickly add up even when eating low-carbohydrate foods. Eating too much carbohydrate or protein and/or not enough fat will increase glucose concentration in the blood and kick you out of ketosis.
  • It's low in fiber. Research suggests the keto diet may negatively affect the gut microbiome, which may be related to a low intake of fiber on the keto diet.11
  • It may negatively affect blood lipids.Depending on the individual, this pattern of eating may affect cholesterol and blood lipids in a negative way, which is why close monitoring by a physician is recommended. However, recent studies show significant benefits in blood lipid profiles.7
  • It may lead to vitamin and mineral deficiencies. This way of eating can contribute to osteoporosis and osteopenia.12 Consider a daily multivitamin.

What You CAN'T Eat on the Keto Diet

The ketogenic diet reduces or severly limits the followin foods:

  • Sweets or any foods containing sugar
  • Grains and bread products
  • Beans and legumes
  • Starchy vegetables (such as potatoes, sweet potatoes, beets and corn)
  • Fruits (except a small quantity of berries)
  • Low-fat dairy products (higher fat dairy can be used in moderation)
  • Many condiments that contain sugar (salad dressings, ketchup)
  • Store bought sugar-free baked goods (because they often contain high amounts of carbohydrates)

What You CAN Eat on the Keto Diet 

  • Meat (a moderate amount)
  • Eggs
  • Fish
  • Avocados
  • Nuts and seeds
  • Butter
  • Cheese
  • High-fat dairy products (a moderate amount)
  • Oils (olive, coconut, avocado)
  • Non-starchy vegetables (broccoli, kale, cauliflower, celery) 
  • Herbs and spices
  • Salt and pepper

What Makes a Recipe Keto-Friendly?

Technically, all foods are keto friendly—it’s just a matter of portion size. But who wants to eat a piece of cake the size of a sugar crystal, right?

So, in general, keto recipes:

  • Strictly limit high-carbohydrate foods
  • Moderately limit protein because protein can be turned into glucose in the body and kick you out of ketosis
  • Contain a large amount of fat to provide adequate calories when carbohydrate and protein are restricted

Specifically, keto recipes provide approximately 5-10% of calories from carbohydrates, about 15-30% of total calories from protein, and about 55 to 80% of total calories from fat (calculated from the difference in carbohydrate and protein).13

If you eat 2,000 calories per day, a keto meal plan would contain approximately:

  • Carbohydrates—25 to 50 grams per day
  • Protein—75 to 150 grams per day
  • Fat—133 to 178 grams per day

“Macros” is short for macronutrients and refers to the three main nutrients that provide energy: carbohydrates, protein and fat. While it’s not absolutely necessary to calculate the macros of every meal while attempting a keto diet, it is very difficult to be sure you are in the range for ketosis any other way.

You can measure your ketone levels in urine with ketone test strips, but hydration status and the longer you are in ketosis can make the results inaccurate. Blood tests for ketone bodies are more accurate, but of course there is a higher cost with blood testing and you have to prick yourself. Calculating your macros is a tedious, but inexpensive method to verify your meal plan is truly keto-friendly.

The Keto Flu and Other Considerations

The first few days of a keto diet are sometimes referred to as the “keto flu” as you notice your body adapting to using fat instead of glucose for fuel.

Be sure to drink plenty of water and sometimes it is helpful to drink broth (which many people find to be surprisingly satisfying) to replace sodium you are losing. You may also notice a fruity acetone smell on your breath—another outcome of your body adopting to ketosis.

All is NOT Lost if a Keto Diet Isn't Right for You

Do what you can! The best way to determine what’s right for you is to test your blood sugar before and after a meal. The average American diet can contain 225 to 325 grams of carbohydrate according to the Dietary Guidelines for Americans, while a keto diet contains fewer than 50 grams.

This leaves a lot of room for a more moderate reduction in carbohydrates. A “lower” carbohydrate (as opposed to a “keto”) diet is often enough of an improvement to manage weight and blood sugar in many people—without the severe restriction of many real foods and the meticulous calculations at each meal. It is important to find a supportive doctor and registered dietitian who can help you personalize the right approach for managing your blood sugar.

The Bottom Line

The keto diet is not for everyone. But if viewed as part of a low-carb lifestyle, a keto diet could be beneficial for some people with diabetes if the benefits outweigh the risks. If you are interested in following the keto diet, it is best to first discuss it with your doctor.

Make sure your doctor is aware of your carbohydrate intake when prescribing medications that have the potential for low blood sugar (hypoglycemia). You will also need to test your blood sugar several times per day. In addition, you should regularly have blood work drawn to assess any changes in your health status. Finally, seek out the help of a registered dietitian and certified diabetes educator to receive support and ensure you are following a nutritionally-balanced approach.

Updated on: July 29, 2019
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