The Ketogenic Diet: An Objective Guide To Its Potential Effects

Ketogenic diets have become popular over the past decade or so, with people typically following them either as a medical diet or for weight management.

However, it’s often difficult to find nuanced and objective coverage of the ketogenic diet online. Some of the claims you see may be grounded in science, but unfortunately many are not.

The truth: Like most specific diets, the ketogenic diet may have some legitimate benefits, but it may also have some drawbacks for your health.

This article provides a complete guide to ketogenic diets, looking at what they are, how they are formulated, and what the scientific research says. As part of this, we’ll assess scientific findings on the ketogenic diet’s impact on blood sugar, cholesterol, weight management, and more.

What Is a Ketogenic Diet?

Ketogenic diets, also known as “keto” for short, involve limiting dietary carbohydrate to low intake levels.

However, accurately describing a ketogenic diet very much depends on the specific definitions we are using.

The diet was first mentioned by name in the 1920s, when it was introduced as a potential treatment for epilepsy. This form of the ketogenic diet is sometimes referred to as a ‘classic ketogenic diet’ (or CKD for short). It was a dietary intervention characterized by a fat consumption that could be as high as 90% of energy intake.

The term ‘ketogenic diet’ was reportedly first used by a highly-regarded diabetes researcher named Russel Wilder in 1921.

In contrast, the modern and popularized ‘keto diet’ tends to focus more on carbohydrate restriction than absolute fat intake, and it can be higher in protein. In this respect, it is quite similar to the Atkins diet that enjoyed its peak of popularity during the 1990s and early 2000s.

This modern interpretation of the ketogenic diet involves high intakes of protein and fat and a low enough carbohydrate intake to enter a state commonly referred to as nutritional ketosis. For the purpose of this article, it is this popularized version of the ketogenic diet that we’ll focus on.

Ketogenic diets fall within the broader low-carbohydrate category of diets, but they restrict carbohydrate intake to a very low level.

An all animal-based food diet has become popular over recent years called the carnivore diet, which also falls within this category. There is very little research on this diet. However, depending on how you define a ketogenic diet, carnivore-style diets could potentially be classed as a type of keto diet.

What Is Ketosis?

Ketosis is a metabolic state that the body enters in response to low glucose availability. The cause is usually a sustained low carbohydrate intake, but other factors, such as high activity levels, can also play a role.

The exact degree of carbohydrate restriction necessary to induce ketosis can vary. However, some researchers have stated that 50 grams of carbohydrates per day tends to be the approximate ‘upper limit.’

For your reference, 50g of carbohydrates is approximately equal to only one of the following:

• 2 medium bananas (53.8g)
• 1 cup (186g) of cooked white rice (53.2g)
• 2 slices of thick white bread (42.4g)

With this level of carbohydrate restriction, the body’s glycogen levels (stored glucose) deplete to a level that are no longer capable of supporting energy requirements. At this point, two metabolic processes begin in the body, known respectively as gluconeogenesis and ketogenesis:

• Gluconeogenesis: Gluc (glucose/sugar) + neo (new) + genesis (formation): Gluconeogenesis simply means the formation of new sugar. In gluconeogenesis, the body begins producing glucose from lactate, glycerol, and the amino acids (proteins) alanine and glutamine.

Put simply; gluconeogenesis means the formation of new sugar.

The body can produce glucose from lactate, glycerol, and the amino acids alanine and glutamine in this manner.

Ketogenesis: keto (ketone bodies) + genesis (formation)

Ketogenesis refers to the formation of ketone bodies. Ketone bodies are a type of molecule that the body can use for energy, and they are produced in the liver from fatty acids.

In other words, you could say that ketosis is the state in which the body burns fatty acids for energy generation rather than relying on glucose.

Macronutrient Ratios

As mentioned, limiting carbohydrate intake to around 50 grams per day tends to be the main feature of a ketogenic diet.

However, according to a 2024 study on low-carbohydrate nutritional considerations, a well-formulated ketogenic diet should contain between 1.2–2.0 grams of protein per kilogram of body weight.

What Ratio of Carbohydrate, Fat, and Protein Might Ketogenic Diets Have?

Based on the above protein levels (1.2g–2.0 per kg of bodyweight), a ketogenic diet could feasibly look like any of the following options. These examples are based on a body weight of 75kg (168 lbs) and a typical 2,000 calorie diet.

• 10% carbohydrate, 70% fat, 20% protein
• 10% carbohydrate, 65% fat, 25% protein
• 10% carbohydrate, 60% fat, 30% protein
• 5% carbohydrate, 75% fat, 20% protein
• 5% carbohydrate, 70% fat, 25% protein
• 5% carbohydrate, 65% fat, 30% protein

Note: If you are following a ketogenic diet for medical reasons (such as epilepsy or type 2 diabetes) it is important to consult with your healthcare provider for individualized dietary advice and not rely on generic ratios.

Is a Ketogenic Diet Right For You?

If you ask someone whether trying a ketogenic diet is a good idea, you will often get an answer based on their personal opinion.

However, the correct response should always consider the individual and their unique requirements, which would ideally look more like this:

• For what reason are you interested in ketogenic diets?
• Can you enjoy the foods available on a carbohydrate-restricted diet?
• What kind of foods do you most enjoy?
• Is a ketogenic diet necessary for your goals?
• Are there any medical issues to be aware of?
• What did you hear about the diet that made you interested in it?

For instance, if you enjoy a diet featuring liberal amounts of fruit, legumes, and root vegetables, then a ketogenic diet is unlikely to be the right fit.

On the other hand, if you find it easier to stick to a way of eating that limits carbohydrates, a lower-carb diet could be worth looking into. A ketogenic diet is one potential option in that area.

However, ketogenic diets are restrictive, limit many popular foods, and may have some health drawbacks (that we’ll explore later). For these reasons, ketogenic diets may not be the right choice for most people.

Note: Anyone with a medical issue should always speak to their healthcare provider before implementing any dietary change. This is imperative as drastic dietary changes can influence health markers and may result in modified medication requirements.

Meal Examples

Despite popular belief, a “keto diet” can include small amounts of higher-carbohydrate foods. This is because there is really no such thing as a “keto food” and it is the overall daily carbohydrate intake that is the most relevant consideration.

For example, even if someone ate a small amount of brown rice and no other carbohydrates that day, the diet would still likely be “ketogenic” if overall carbohydrate intake was sufficiently restricted.

That said, if aiming for a total daily carbohydrate intake of >50 grams, a “keto meal” would likely contain less than 20 grams of carbohydrate as an upper limit.

What Kind of Meals Can You Eat On a Ketogenic Diet?

Based on the aforementioned 20-gram carbohydrate limit, here are some meals that fit into this modern interpretation of a keto diet.

Next to each meal, you can see the meal’s macronutrient content, with all values calculated using data from the USDA’s FoodData Central and based on meals being prepared using the raw weights listed.

Please note: These meal options are based on typical ketogenic meals and a focus on including a wide range of food options. While some may be nutrient-rich, they are not specifically intended as “healthy meal” recommendations.

• Eggs, salmon, spinach, and mushrooms: 2 large eggs, 4 oz (112g) salmon, 3 oz (85g) spinach, 3 oz (85-gram) mushrooms, 2 tbsp olive oil [653 calories, 6.6g carbohydrate, 52.2g fat, 40.5g protein]
• Cottage cheese, almonds, Cheddar cheese, and strawberries: 1 cup (210g) cottage cheese, 1 oz (28g) almonds, 1 oz (28g) Cheddar cheese, 1/2 cup (76g) strawberries [506 calories, 20.0g carbohydrate, 32.9g fat, 36.3g protein]
• Beef, broccoli, and carrots: 4 oz (113g) ground beef, 1 cup (91g) broccoli, 1 cup (128g) diced carrots, 2 tbsp olive oil [594 calories, 18.3g carbohydrate, 43.9g fat, 33.2g protein]
• Mackerel, mushrooms, edamame, and spinach: 1 fillet of mackerel (115g), 3 oz (85g) mushrooms, 4 oz (113g) edamame, 4 oz (113g) spinach, 1 tbsp olive oil [539 calories, 17.2g carbohydrate, 36.1g fat, 41.0g protein]
• Tofu, canned tomatoes, and bell pepper: 1 cup (252g) cubed tofu, 1/2 cup (121g) canned crushed tomatoes, 1 medium red bell pepper (119g), 1 tsp soy sauce, pinch of herbs and spices [467 calories, 20.0g carbohydrate, 31.8g fat, 36.6g protein]
• Bacon, eggs, grilled tomato, and mushrooms: 3 slices bacon, 2 large eggs, 1 medium grilled tomato, 3 oz (85g) mushrooms [524 calories, 17.9g carbohydrate, 38.5g fat, 31.0g protein]
• Cheese and leak omelet: 3 large eggs, 1 oz (28g) Cheddar cheese, 2 oz (56g) chopped leek, 1 tbsp olive oil [483 calories, 10.1g carbohydrate, 37.4g fat, 26.2g protein]
• Cheeseboard style meal: 1 oz (28g) Cheddar cheese, 2 oz (56g) prosciutto, six (24g) green and black olives, 1 oz (28g) walnuts, 1 cup of strawberries (152g) [477 calories, 18.0g carbohydrate, 32.9g fat, 27.8g protein]
• Sardine and cheese salad: 1 tin of sardines canned in olive oil (140g), 1 oz (28g) feta cheese, 3 oz (85g) arugula, 1 cup cherry tomatoes, 1 small red onion (sliced), 1 medium yellow bell pepper (119g) 1 tbsp olive oil, 2 tsp balsamic vinegar [594 calories, 19.2g carbohydrate, 44.8g fat, 30.9g protein]

As shown in the above examples, ketogenic diets can incorporate a broad range of animal-based and plant-based foods.

Note: Changing the serving quantities is a simple way to adjust the amount of carbohydrate, fat, or protein.

Potential Benefits

Large studies involving human participants have demonstrated that ketogenic diets may have several potential health benefits.

In the next few sections, we’ll review some of the recent positive findings on ketogenic diets.

Ketogenic Diets and Weight Management

Several large studies have looked into the effects of a ketogenic diet on weight loss.

Some of these studies have also compared very low carbohydrate ketogenic diets to a low-fat control group dietary intervention control group.

Randomized controlled trials have consistently demonstrated that (9, 10, 11, 12, 13, 14, 15):

• Ketogenic diet weight loss interventions are generally successful and mostly lead to weight loss, at least in the short term. The vast majority of studies show significant weight loss during the intervention in a wide range of populations.
• Despite ketogenic diets and low-fat diets both leading to weight loss, short-term weight loss tends to be slightly (but not significantly) higher with low-carb ketogenic diet interventions. However, this weight loss becomes less significant at the 12-month mark, with some clinical trials noting a slight benefit either way and some seeing no difference (16, 17, 18).

Adherence To the Diet Is Key

The scientific literature is clear that it is difficult to achieve and sustain weight loss with any diet in the long-term. All diets are notoriously difficult to adhere to in the long-term, and it is common for individuals to give up their chosen diet and regain lost weight (19).

Unfortunately, this trend is common with ketogenic diets too. Numerous randomized controlled trials show that it is common for carbohydrate intake to increase over the course of longer-term ketogenic diet interventions. This increased carbohydrate intake happens as adherence to the diet falls and weight loss plateaus.

We can see a good example of this in a recent meta-analysis of therapeutic ketogenic diet interventions for patients with epilepsy. This meta-analysis found that over 12 studies featuring 270 participants, the average adherence rate to a ketogenic diet was only 45% (20).

One point to note here is that these individuals weren’t choosing the diet because they wished to enjoy a ketogenic diet way of eating. It was a therapeutic intervention that they may not have had an enthusiasm for.

As this example shows, a ketogenic diet must be the right fit for the individual. If someone enjoys their particular way of eating, they can likely sustain their diet for the long term. On the other hand, if it is a constant struggle to maintain a way of eating, long-term adherence is doubtful.

This is why so many people try various “yo-yo” diets, regain weight, and try a new diet.

The key to a good, sustainable way of eating is a diet that you enjoy.

Additionally, here are some common reasons why people may struggle losing weight with a ketogenic diet.

Alzheimer’s and Cognitive Health

Several studies have examined the potential effects of a ketogenic diet for treating conditions such as Alzheimer’s and wider cognitive health.

A lot of this research has been driven by the fact that Alzheimer’s leads to impaired glucose metabolism in the brain (21).

Since ketogenic diets encourage the body to switch from using glucose to ketone bodies as the main fuel source, researchers have been examining if there may be any potential benefits from the diet for individuals with Alzheimer’s and dementia.

On this note, several small clinical trials have suggested that ketogenic diets may potentially increase the quality of life and cognitive performance of Alzheimer’s patients and older adults with cognitive impairments (22, 23, 24).

However, it should be noted that this is an emerging field of study. Further research in larger populations and over more extensive timeframes is necessary to investigate this area better.

Type 2 Diabetes

Much research has been conducted on very-low-carb ketogenic diets and their potential for helping to treat/manage type 2 diabetes.

Among this research, a recently published meta-analysis of clinical trials investigated the use of ketogenic diets for managing glycemic (blood sugar) control (25).

This review identified that, as a therapeutic intervention, ketogenic diets consistently led to improved blood sugar control without negatively affecting blood lipids/LDL cholesterol. Also, the ketogenic diet tended to outperform control diets in this area (25).

A recent systematic review and meta-analysis demonstrated that low carbohydrate diets appear to have a “greater effect on glycemic control in type 2 diabetes compared with high-carbohydrate diets in the first year of intervention” (26).

Of course, ketogenic diets are not the only valid dietary approach for type 2 diabetes, and different approaches can work equally well. Whether the diet in question drives weight loss seems to be the most important aspect for type 2 diabetes management/remission (27).

Note: It is worth remembering that individuals with type 2 diabetes should always discuss their physician/primary medical team before considering any significant dietary change.

Epilepsy

Ketogenic diets have been used as therapeutic dietary interventions for epilepsy since the early 1900s.

An extensive amount of research supports ketogenic diets for this purpose (28, 29, 30, 31, 32).

Other Medical Conditions

Research is ongoing concerning ketogenic diets and other medical conditions, such as various cancer types (33).

However, the evidence base is lacking, and it does not support any health claims in this area.

It is possible that ketogenic diets may help with certain conditions, and it is equally possible that they may harm. This will remain the case until adequate evidence from human trials is available to either support or contradict the use of ketogenic diets in such areas.

Potential Drawbacks

The obvious drawback to ketogenic diets is that they restrict carbohydrate intake, which automatically limits a wide range of (potentially) nutrient-rich foods.

But are there any other concerns above and beyond the carbohydrate restriction?

Three of the most common criticisms of ketogenic diets are listed below:

• “Ketogenic diets may raise LDL cholesterol levels.”
• “The diet lacks dietary fiber.”
• “Ketogenic diets cause ketoacidosis.”

Is there any truth to these criticisms? And if so, is there anything that can be done about them?

Let’s take a look.

Ketogenic Diets, LDL Cholesterol, and Blood Lipids

Ketogenic diets tend to be very high in fat, of which saturated fat can sometimes form a significant proportion.

Certain saturated fatty acids, particularly palmitic acid and myristic acid, can lead to increased LDL cholesterol (LDL-C) levels. Palmitic acid and myristic acid can mainly be found in animal fats like butter as well as palm oil (34, 35).

Despite much debate on the topic, an extensive systematic review and meta-analysis of LDL-lowering interventions demonstrated that “lower achieved LDL-C levels were associated with lower rates of major coronary events” (36).

A Cochrane systematic review of 15 randomized controlled trials also noted that long-term lowering of saturated fat intake helped prevent cardiovascular events (37).

However, ketogenic diets do not necessarily have to raise LDL levels. The diet’s effect on LDL levels appears to be variable, with some human trials suggesting that ketogenic diets can significantly raise LDL, but others showing little effect (38, 39, 40).

On this note, a recent scientific statement by the National Lipid Association, published in the Journal of Clinical Lipidology, noted that these varying effects might depend on “the quality of the diet interventions in the randomized clinical trials” (41).

Specific Foods Have Different Effects on LDL Levels, Thus the Diet’s Effects Are Variable

It is always a sensible idea to check markers of health with a doctor after a significant dietary change, but here are some considerations if LDL levels are a concern:

• Lean cuts of meat and seafood options, including fish and shellfish, will not influence LDL levels in the same way that fattier cuts of meat will (42).
• Randomized controlled trials show that cream and cheese do not raise LDL levels compared to butter (or compared to baseline diet). These foods have an intact milk fat globule membrane (MFGM) that encapsulates the fatty acids; this MFGM is broken in the churning process to produce butter (43, 44).
• Most nuts are compatible with ketogenic diets, and clinical trials suggest that they can lower LDL levels and improve overall cardiovascular health markers (45, 46, 47).
• Seeds and seed products such as flax seeds and psyllium husk can significantly lower LDL levels. This is mainly due to their respective polyunsaturated fat and fiber content (45, 46).
• Polyunsaturated fats and fiber can both, in general, lower LDL levels. This is particularly true for polyunsaturated fats when they are a substitute for saturated fats. These nutrients are found in nuts and seeds and in food such as avocados, which can also lower LDL (47, 48, 49).

In short, the impact of a ketogenic diet on LDL levels will depend on the specific diet being followed and the individual.

As a very simplistic summary:

• Increasing saturated fat and lowering fiber and polyunsaturated fats could be anticipated to increase LDL levels.
• Lowering saturated fat intake and increasing fiber and polyunsaturated fat may lower LDL levels.
• Consuming foods/meals high in both fiber and saturated fat may potentially have a neutral effect. An example of this can be seen with coconut flakes, which are high in saturated fat and fiber yet appear to lower LDL levels (50).

Ketogenic Diets and Fiber

Higher fiber intake is consistently associated with health benefits, including lower mortality, across multiple lines of evidence from extensive observational studies to large human trials (51, 52, 53).

It is a common claim that ketogenic diets lack fiber.

Firstly, it is certainly true that ketogenic diets can be low in fiber. However, it is also very possible to consume large amounts of fiber on such diets.

Here are some high-fiber foods that can fit into a ketogenic diet (the fiber values are for raw weight, and they are sourced from the USDA database):

• Almonds: 12.5g fiber per 100g (54)
• Cocoa powder: 37.0g fiber per 100g (55)
• Artichoke: 5.7g fiber per 100g (56)
• Avocado: 6.7g fiber per 100g (57)
• Blackberries: 5.3g fiber per 100g (58)
• Brussels sprouts: 3.8g fiber per 100g (59)
• Chia seeds: 27.3g fiber per 100g (60)
• Flax seeds: 27.3g fiber per 100g (61)
• Hazelnuts: 9.7g fiber per 100g (62)
• Kale: 4.1g fiber per 100g (63)
• Lupin beans: 37.5g fiber per 100g (64)
• Pecans: 9.6g fiber per 100g (65)
• Psyllium husk: 78g fiber per 100g (66)
• Raspberries: 6.5g fiber per 100g (67)
• Spinach: 2.2g fiber per 100g (68)

Ketoacidosis

Some people claim that ketogenic diets are unhealthy because they “cause ketoacidosis,” but such statements, taken definitively, are largely incorrect.

As previously mentioned, ketosis is a physiological state in which the body starts to burn ketones (fats) for energy instead of glucose.

In contrast, ketoacidosis is a potentially life-threatening condition that occurs when the body doesn’t make enough insulin, and thus ketone levels become abnormally high.

A small amount of insulin is released in healthy people to stop ketone levels from becoming too high. However, individuals with type 1 diabetes do not produce sufficient insulin, and thus poor management of type 1 diabetes can lead to excessive ketone levels, leading to ketoacidosis (69, 70).

However, in healthy individuals following low-carb diets, the production of ketones is “regulated and controlled” and thus should not lead to ketoacidosis (71).

That said, it is worth pointing out that there have been reports of ketoacidosis occurring on carbohydrate-restricted diets in certain population groups:

• Lactating women (72, 73, 74)
• Individuals with type 2 diabetes who were using a class of medicines known as SGLT2 inhibitors (75, 76, 77)

Again, anyone making a significant dietary change (particularly if a medical condition is present) should discuss it with their doctor.

See this guide to ketogenic diets and ketoacidosis for more information.

Other Potential Side Effects To Consider

Starting a ketogenic diet can be difficult due to changes that occur during the first week or so of following the diet. These changes may include losses of water weight as insulin levels drop (and thus electrolytes), and “adapting” to the diet can cause unwanted symptoms.

According to published research, these symptoms may include dizziness, lethargy, lightheadedness, and nausea. These self-reported symptoms tend to last anywhere from a few days to a few weeks (78, 79).

Note: It is important not to assume an adverse effect is “normal” – always consult your healthcare provider if any side effects occur from a diet.

Foods Compatible With a Ketogenic Diet

As previously mentioned, the most important consideration with ketogenic diets is the total carbohydrate intake rather than specific foods.

However, ketogenic diets typically focus on the types of foods listed below (with some examples where applicable):

• Cooking fats and oils: Avocado oil, butter, canola oil, olive oil
• Dairy: Cheese, cream, yogurt
• Drinks: Coffee, diet soda, herbal tea, tea, water
• Eggs
• Fish
• Fruit: Low-sugar options like avocado and berries
• Meat
• Nuts: Almonds, hazelnuts, macadamia nuts, pecans
• Poultry
• Seeds: Chia seeds, flaxseeds, pumpkin seeds
• Shellfish
• Vegetables: Especially mushrooms and leafy greens

Note: For a more in-depth guide to keto-friendly foods, see this keto shopping list with carbohydrate data for each food.

Keto Snack Options

Popular snack options like potato chips and milk chocolate don’t fit a ketogenic diet. Here are some “snack” options that are suitable for keto:

• Berries and yogurt: Your choice of berries in a bowl with some yogurt.
• Boiled eggs: A boiled egg or two is a satisfying protein-rich snack.
• Celery and cream cheese: Spread some cream cheese on a few stalks of celery. Some alternatives to cream cheese could include peanut butter, harissa, or hummus.
• Cheese: A quick, convenient, and nutrient-rich snack.
• Dark chocolate: The higher the cocoa content, the better. Dark chocolate bars with a cocoa percentage of 85% or more will contain the lowest sugar levels.
• Guacamole salad: Mash up some guacamole and mix it with some leafy greens and cherry tomatoes.
• Jerky: Meat or fish jerky is a convenient protein-rich snack for a ketogenic diet.
• Nuts and seeds: A handful of nuts provides a good amount of protein, fat, fiber, vitamins, and minerals.

Foods To Limit/Avoid

Due to the nature of ketogenic diets, most high-carbohydrate foods are unsuitable for this way of eating.

Below is a list of the foods and drinks that are generally too high in carbohydrates for a keto diet:

• Beer (most beer except light options)
• Cakes
• Cookies
• Dried fruit (a small amount is OK, but the carbohydrate levels will quickly add up)
• Fruits high in carbs (banana, mango, papaya)
• Fruit juice
• Grain products (bread, cereals, pasta)
• Legumes (such as beans and lentils)
• Milk (a small amount is OK, but milk has about 12g carbs per cup)
• Sugary foods and sugar-sweetened products in general
• Sweet wines/sugary alcohol
• Tubers such as parsnips, potatoes, and sweet potatoes
• Whole grains (such as barley, oats, and wholewheat)

For those who drink alcohol, dry wine and spirits tend to be the lowest-carbohydrate options.

Final Thoughts

Research over recent years is clear that ketogenic diets can have various benefits, ranging from weight loss to type 2 diabetes management.

Despite this, the effects of the diet are often over-hyped and exaggerated, and it is just one of many suitable dietary interventions for such conditions.

Lower carbohydrate diets that allow a more moderate carbohydrate provision can be equally effective, as can other dietary patterns.

For those who don’t mind the level of carbohydrate restriction required and enjoy low-carb foods, a well-formulated ketogenic diet might be worth investigating.

Lastly, it is worth pointing out that many of the foods that fit with ketogenic diets are not staple foods, thus the diet can be expensive.

This article on nutrient-rich yet affordable foods provides some budget-friendly food choice ideas, many of which can fit into a ketogenic diet.