The Ketogenic Diet and Diabetes: The Definitive Guide

The ketogenic diet (“keto”) has been around for a LONG time. It’s popular. It’s controversial. Some love it. Some hate it. Some even say it can help your blood sugar levels stay in better control.

After thoroughly reviewing the scientific literature and trying the ketogenic diet myself for over six months, I am ready to explore everything you’ve been hearing and let you decide for yourself what you think about the diet that has taken the world and diabetes community by storm.

This guide is relevant for people with any type of diabetes. I will mainly talk about insulin when I discuss how a keto diet affects blood sugar, but some studies also show a possible reduction in certain type 2 medications. 

Disclaimer: Please always consult with your medical team before you start a new diet, adjust your medication, or change your diabetes management routine.

What is a ketogenic diet?

Once upon a time, keto was the original “diabetes diet” prescribed to people with type 1 diabetes before the discovery of insulin. This would prolong their lives, as the diet is less likely to raise blood sugar levels due to its low carbohydrate content. (Carbohydrate is the main nutrient that raises blood sugar levels.)

The ketogenic diet is a low-carb diet where you get only about 5 percent of your daily caloric intake from carbohydrates. By restricting your carbohydrate intake so severely, you force your body to get most of its energy from fat. A byproduct of this fat burning is the production of natural ketones in the body, hence the name of the diet.

Burning ketones supplies the body with an alternative form of energy rather than quickly accessible energy from carbs (glucose) and is what makes the ketogenic diet work. (IMPORTANT: Natural ketones are different from the “bad” ketones that can lead to diabetic ketoacidosis (DKA). More about that later in this guide).

The two main reasons why a person with diabetes would follow a keto diet are:

1. To reduce insulin need and avoid blood sugar fluctuations
2. To aid weight management (weight loss)

In the rest of this guide, I will review the pros and cons of a keto diet and try to answer the obvious question: “Is a keto diet good for people with diabetes?”

What foods are recommended for a keto diet?

Some sample foods recommended for this diet include:

• Meats (e.g., beef, pork, lamb, poultry, and game meats; preferably grass-fed and organic, if possible)
• Fatty fish (e.g., salmon, mackerel, sardines, trout, and other fish rich in omega-3 fatty acids)
• Eggs (preferably free-range or omega-3-enriched eggs)
• High-fat dairy (e.g., butter, cream, and certain cheeses)
• Nuts and seeds (e.g., almonds, walnuts, flaxseeds, pumpkin seeds, chia seeds)
• Healthy oils (primarily extra-virgin olive oil, coconut oil, and avocado oil)
• Avocados (whole avocados or freshly made guacamole)
• Low-carb vegetables (e.g., green veggies, tomatoes, onions, peppers)
• Condiments (e.g., salt, pepper, herbs, and spices)
• Beverages (e.g., water, unsweetened coffee and tea)

A dietitian can help you figure out the best combination of foods to eat, taking into consideration your lifestyle and overall health goals.

How much fat, protein, and carbs to eat on a keto diet

To follow a keto diet, you’re looking at approximately this split in daily calorie intake:

• 75 to 85 percent fat
• 10 to 20 percent protein
• 5 percent carbohydrate, or less than 20 to 50 grams per day

As an example, if we converted this to grams for a person on a 2,000-calorie diet, this equals:

• 167 to 189 grams of fat
• 50 to 100 grams of protein
• 25 grams of carbohydrates

NOTE: I am NOT saying that you should eat a 2,000-calorie diet. This is just an example! Please read this post to learn how to calculate your daily calorie need.

Protein is key here, because in the absence of carbohydrates, protein can be converted into glucose via gluconeogenesis (formation of new glucose within the body). Since it is glucose, it can kick you OUT of ketosis. So it’s important not to overdo your protein if you want true ketosis.

I will be spending the rest of the article talking from the 20 to 50 grams of carbs and moderate protein (about 20 percent) perspective. When I tried the keto diet, I was able to eat that quantity of carbohydrates and up to 150 to 160 grams of protein per day and remain in ketosis. Results may vary.

How does a keto diet affect blood sugar?

The premise of the ketogenic diet and diabetes is easy: fewer carbs require less insulin and should result in fewer blood sugar spikes. Fewer blood sugar spikes should lead to improved time in range and better A1c values (a measure of glucose control over the previous 2 to 3 months).

In addition, several studies have shown that the keto diet can improve insulin sensitivity, further reducing the need for insulin and making blood sugar control easier.

IF (and that is a big if) you can adhere to it, keto can be a very effective way to manage your blood sugars. The swings will truly start to dissipate, trendlines on CGMs will flatten, and your A1c will quite possibly drop. I had the best A1c of my LIFE while doing keto.

On the flip side, hypos (low blood sugar) can be an issue, especially early on … and if you treat them too aggressively, they could knock you out of ketosis. I remember my first three weeks on keto, my CGM trend line hugged a blood sugar of around 80. It was glorious, but I had to reduce insulin substantially through trial and error and felt like I was low every five seconds.

When I would overtreat a low, I would sometimes push my carbohydrate amount over the keto threshold and end up OUT of ketosis … not that it is the worst thing in the world, but the goal is to remain in ketosis as much as possible.

That keto diets work in real life is exemplified by the fact that the keto diet is perhaps the most popular low-carb diet for people with diabetes and that thousands (if not hundreds of thousands) of people swear by the keto diet for good blood sugar management.

HOWEVER …

There are also a significant number of people (including Christel Oerum, the owner of Diabetes Strong) who experience the opposite reaction to the keto diet. Instead of increased insulin sensitivity, they experience a drastic increase in their insulin resistance, meaning that they need large amounts of insulin even for a very small amount of carbs.

This phenomenon has not been studied scientifically, but there is enough anecdotal evidence to suggest that not everyone reacts the same to a keto diet, and it may be unsuitable for some people.

Verdict: The keto diet can be very effective for blood sugar management, but there is significant variation between individuals. It does not work for everyone, but with the OK from your healthcare team, it could be worth trying to see how it works for you.

Is a keto diet effective for weight loss?

Given that the whole idea of the keto diet is to burn fat instead of carbs for energy, it seems logical that the keto diet should be effective for weight loss. While this is also often the case, it’s important to remember that the basic mantra of weight loss still applies:

Calories in (eating) < Calories out (burning) = weight loss

If you eat more calories than you burn, you will gain weight — no matter what type of diet you follow. To learn more about how many calories to eat, please see my post How to Lose Weight With Diabetes and follow the steps in the post How to Find Your Daily Calorie Need to calculate your optimal daily calorie intake.

The theory behind using a keto diet for weight loss

Proponents of using a keto diet for weight loss argue that eating carbs drives up insulin production, which increases hunger and causes the body to hold on to fat and suppress calorie burn. When you replace carbs with fat, you decrease the need for insulin, subdue hunger, boost calorie burn, and melt away fat.

Many people also report fat as very satiating, making them feel full. The same goes for protein. When you feel full, you eat fewer calories and have fewer cravings. When you are at a healthy caloric deficit, you are primed to lose unwanted pounds.

What the science says…

Several comprehensive studies and meta-analyses (analyses of data from several studies) have demonstrated that after a few months or even a year of a low-carb diet versus a moderate-/high-carb diet, there are no significant differences in the amount of weight lost. 

I will say, however, that most of these diets are NOT keto and are simply lower carb (i.e., 20 percent). Also, long-term effects (beyond one year) are not often studied due to budgetary constraints, so interpret results as you wish.

Verdict: A keto diet is not inherently better for weight loss than other diets but can be very effective if it:

• Helps you manage your blood sugar better than other diets
• Is easier for you to follow than other diets
• Works for your general lifestyle

As with most other diets, the main criteria for success is whether or not you can follow the diet for the long term. If you like the keto lifestyle, the diet can work great. If you hate it, it probably won’t work for you.

A quick note on keto and water retention

You often hear people who start a keto diet exclaim, “I’ve been keto for a week, and I’ve already lost 6 pounds! I love it!”

While this can be a great motivator to stick to the diet, most of that initial weight loss consists of water due to less glycogen storage (glycogen is the storage form of glucose).

Why? The old saying goes, “wherever glycogen goes, water follows.”

Because you eat fewer carbs, you will have fewer glycogen stores. Less glycogen means less water retained. Less water retained and, you guessed it … the scale goes down. There is nothing wrong with that — just don’t mistake lost water weight for fat loss.

Keto diet and exercise

Starting on a ketogenic diet can influence your exercise performance in multiple ways, both positive and negative. During the first one to two weeks (the “adaptation period,” which I will get back to later), you will most likely see a decrease in energy and athletic performance across the board while your body adjusts to the new diet. 

This is perfectly normal and should NOT be a cause for concern or make you abandon the diet.

When your body has adapted to the ketogenic diet, you will most likely experience that cardio returns to its previous level of difficulty, but strength training may or may not be harder.

You have access to more energy for cardio

Your body stores a lot more energy as fat than it does as glycogen. A keto diet allows you to tap into that reservoir of stored fat energy more easily.

This is why you sometimes hear about endurance athletes who have successfully switched to keto and continued to perform at a high level because they no longer hit the metaphorical “wall.” They have access to a gigantic reservoir of fuel that was previously more difficult and took longer to access.

Strength may suffer, at least for a while

This is ESPECIALLY evident during adaptation, but keto is not really ideal for high-intensity physical activity. Biochemically, this makes sense — intensive bouts need energy quickly, and fat oxidation is not exactly the fastest process in the world.

There is hardly any scientific data on keto diets and strength training, but plenty of anecdotal evidence states that it can be difficult to even maintain strength.

Personally, all of my lifts dropped 40 to 50 pounds for the first four to six weeks after I switched to a keto diet. Weights that I used to toss around with ease became tougher to move until I was fully adapted.

It’s not impossible to improve strength while on a keto diet, but it can make the process substantially more difficult.

How difficult is a keto diet to follow?

This is the most important, but also most subjective, question about any diet. If you don’t feel physically and mentally well on a diet, it won’t lead to long-term results, because you won’t adhere to it.

The keto diet is probably one of the most polarizing diets when it comes to people’s opinions on how easy it is to follow. Some people love it almost from day one while others experience major food cravings and even physical discomfort.

This is what my experience with a keto diet was like. Yours may be different:

Keto adaptation is ROUGH

It takes a while to become what is known as “keto-adapted,” which is your body’s way of saying “hey, I got this, I’m ready to mainly burn fat!”

According to keto expert Ariel Warren, RDN, CD, CDCES, the exact length of the adaptation period usually depends on how many carbohydrates you are used to eating. Around two weeks if you have eaten a relatively low-carb diet previously, two to four weeks for a more moderate-carb diet, and four plus weeks for a high-carbohydrate diet.

At the start of the adaptation period, your body is rebooting what it has known for pretty much your entire life. Your brain is used to running on glucose and suddenly it doesn’t have it. Now, it CRAVES it. You’re in glucose WITHDRAWAL.

Some describe this phenomenon as the “keto flu,” where you basically feel the opposite of everything promised — sick, fatigued, nauseous, mentally cloudy, etc. — it’s not very pleasant.

Oh, and I should probably also mention that low carb often means low fiber … pooping could be an issue. It’s often recommended to add extra magnesium, potassium, and sodium to your diet (especially in the adaptation phase) to help your digestion-elimination process.

However, if we look positively, it also means you’re doing something right if you experience this, but … who wants to self-inflict that kind of discomfort? I did, and it was not fun. On this note …

Adherence can be a problem

If you have tried keto (or really any low-carb diet), even for a day, this will probably resonate with you. You hang in through the first few hours. Maybe through the first day. Maybe even day two or three. Maybe it’s been three months. It really doesn’t matter — it is inevitable that eventually, the cravings start … and they are STRONG.

“Oh, I can have some carbs now, it won’t matter much,” you justify to yourself. You cave.

The results are like the pop-up ads on your Internet browser. “Congratulations! You’ve just restarted the keto adaptation process. Anything you previously did is now for naught. Thanks!” *browser closed automatically*

Granted, the longer you’ve been keto, the easier the re-adaptation process, but during that initial transition, it is IMPERATIVE that one maintains the correct macronutrient split or the adaptation will not occur.

Since that process is neither glamorous nor comfortable, not many can push through with near-perfect consistency, myself included.

As you can hear, I found keto to be rough going but, again, your experience may be different.

Is a keto diet safe for people with diabetes?

There haven’t been a lot of studies done on the long-term safety and effectiveness of following a keto diet, especially for people with diabetes, and this is an area of ongoing research. Thus far, it appears to be safe and effective for some people with diabetes.

One of the main risks when following a keto diet (or any other diet that restricts food choice and calorie intake) is related to mental health. ANY restrictive diet can potentially lead to an unhealthy relationship with food, and, in some cases, eating disorders.

If you find yourself constantly thinking about food, avoiding social situations where food is involved, or struggling with a negative body image, please seek professional help.

NOTE: It’s important to stress that this risk isn’t related specifically to a keto diet but dieting in general!

Additional potential risks of the keto diet can include hypoglycemia [low blood sugar] for those on insulin or drugs that promote the release of insulin, nutrient deficiencies, kidney stones, acceleration of kidney damage for those with kidney disease, and constipation.

Keto diet and ketoacidosis

Diabetic ketoacidosis occurs when, in an individual with diabetes, there is an absence of insulin or the presence of illness, infection, or severe dehydration. Blood sugars skyrocket, glucose toxicity occurs, and the blood can turn acidic, hence acidosis.

What a lovely prognosis. This is NOT related to a ketogenic diet. The ketones you develop on a keto diet should never reach dangerous levels, as long as you take the right amount of insulin.

You can easily measure the ketone level in your body with a urine test. You can buy ketone test kits over the counter at most drug stores and pharmacies.

Urine ketone levels

You can also get test kits that use a drop of blood instead of urine. They use a different measuring scale, so please always read the packaging carefully before taking any ketone test.

Keto diet and pregnancy

A ketogenic diet is NOT recommended for women who are pregnant, breastfeeding, or have gestational diabetes. Not because studies have shown that it’s harmful, but because there haven’t been enough studies to show that it’s SAFE!

The diet is also advised against for those with a variety of other health conditions, including pancreatitis, liver failure, and more. Visit the National Library of Medicine for a more comprehensive list.

Final thoughts: Is a keto diet good for people with diabetes?

A keto diet can be very effective for people with diabetes. Some of the potential benefits include:

• Better blood sugar management
• Effective weight management
• A feeling of fullness (fewer cravings)
• More energy for cardio workouts

However, there are large personal differences in how people react to a keto diet, and some experience almost the opposite reaction. I recommend that you try following a keto diet for a while (at least two to three weeks, as the beginning is always hard) to see how it works for you.

If you feel that a keto diet isn’t working for you after trying it, definitely don’t feel compelled to follow it just because so many people with diabetes recommend it. There are many great alternatives. I tried following a keto diet for a while but eventually went back to a more traditional medium-carb diet. It simply works better for me!

I hope this guide has given you a full view of the ketogenic diet and diabetes. At the end of the day, it’s up to you and your healthcare team to decide if you want to try it and see if it has any beneficial effects on your blood sugars, body composition, or just how you feel. If you go for it, a good place to start is with this ketogenic meal plan. Good luck!