Low-carb and ketogenic (keto) diets are popular diets that involve restricting carbohydrate (carb) intake.
To limit carbs, individuals who follow these diets may limit their consumption of grains, legumes, sugar-sweetened snacks and beverages, and even some fruit and vegetables.
Because low-carb and keto diets share several foods and food groups that must be excluded or limited, they are often perceived to be very similar or virtually the same.
I have heard many people state that they are following a keto diet, but when I ask them how it is going, the diet that they describe to me is actually a low-carb diet, not a keto diet. I have also encountered people who think that the keto diet is simply a very-low-carb diet, which is not the case.
While the keto diet is in fact a type of low-carb diet, it is a very specific type of low-carb diet that can help to accomplish specific goals.
Here are three key differences between low-carb and keto diets to consider:
1. Source of Fuel: ATP Synthesis vs Nutritional Ketosis
The central difference between low-carb diets and keto diets is the energy source used by cells in the body. Adenosine triphosphate (ATP) provides energy for the cellular processes that take place in most animal cells.
While fats, proteins, and carbohydrates all help to drive ATP synthesis in the human body, most cells use glucose for ATP synthesis. In fact, nearly all cells can take up and utilize glucose. Red blood cells need glucose for energy, and adipose tissue, muscle cells, and the brain also use glucose for energy, in addition to fatty acids and/or ketone bodies and/or amino acids.
However, when glucose is not readily available, e.g. during prolonged fasting, ketone bodies (ketones) are released in the blood by liver cells and can be used as energy.1 Ketones, compounds produced during the breakdown of fats, include acetoacetate, beta-hydroxybutyrate, and acetone.
Ketones are also produced during nutritional ketosis. As nutrition researcher Chris Irvin, MS succinctly states, “The difference between low carb and keto is nutritional ketosis (NK). NK is a metabolic state where your liver is producing ketones and your brain is using those ketones for energy.”
During a general low-carb diet, the body will still use glucose for fuel, but during NK, ketones are used for fuel. Of note, the body still needs glucose and glycogen during ketosis. Gluconeogenesis is a process in which the liver and kidneys make glucose from non-carbohydrate sources, such as amino acids. Because of gluconeogenesis, glucose remains available in the body even when ketones are being produced.
2. Macronutrient Composition: Low Carb vs Virtually No Carb
While the main difference between the two diets may be the source of fuel primarily used by the body, the most obvious difference to individuals who follow low-carb or keto diets is the ratio of fat to carbs to protein that they consume.
The Dietary Guidelines for Americans (DGA) recommends 45-65% of total daily calories to come from carbohydrates,2 so anything less than 45% is technically low-carb. Some low-carb diets recommend lower numbers, e.g. 10-30% of the diet coming from carbs.
On the other hand, carbs may be limited to 5-10% of total daily calories for keto diets. According to Chris Irvin, MS, “A low carb diet for some can mean anything less than 150g/day but NK won’t occur for many until under 30-50g of carbohydrates.”
A typical meal for a low-carb diet might include meat, butter, carrots, tomatoes, bell peppers, broccoli, and perhaps even some potato. A typical meal for a keto diet might include meat, butter, broccoli, and perhaps a few cherry tomatoes.
As you might be able to tell from the example meals, carbs are the main macronutrient that makes a difference between the two diets. As mentioned, keto diets are a type of low-carb diets in which carb intake is very low. However, fat and protein content vary between the two diets too.
While many low-carb diets are also high-protein diets, the keto diet is high in fat, moderate in protein, and low in carbs. Since ketones are the main fuel source with keto diets, fat is the priority macronutrient to consume.
Many people think that protein should be limited on a keto diet so that it doesn’t interfere with ketosis from amino acids being converted to glucose via gluconeogenesis. However, gluconeogenesis will occur even without high protein intake, so protein intake likely will not make a huge difference.
Moreover, when protein intake exceeds physiological needs for amino acids, the extra amino acids can be disposed of via increased oxidation and enhanced ureagenesis in addition to gluconeogenesis.3 In other words, it is not the case that all excess protein will be used to make glucose.
3. Therapeutic Applications of the Ketogenic Diet
Low-carb and keto diets also vary by the conditions that they are sometimes used to treat. The keto diet has been used to treat epilepsy since the 1920s, and more recently for conditions such as type 2 diabetes, polycystic ovary syndrome, acne, neurological diseases, and cancer.4
On the other hand, the only condition that general low-carb diets are prescribed to help treat is type 2 diabetes (although low-carb diets are certainly not necessary to treat type 2 diabetes).
However, there is evidence that keto diets are more effective for achieving glycemic control in individuals with type 2 diabetes than standard low-calorie diets.5 This may be due to the keto diet causing a benevolent “pseudo-diabetes” that may counteract type 2 diabetes or its complications.6
Thus, the keto diet seems to be the clear winner for potential therapeutic applications.
Considering Keto or Low Carb Dieting?
Before starting a keto or low-carb diet, you should consult with a doctor or work with a registered dietitian to determine what makes the most sense for you and your goals.
If you’re not ready to consult with a professional and simply wondering if a low-carb or keto diet could be right for you, you should decide whether you are willing to cut out a substantial number of foods and potentially even entire food groups. If you don’t mind cutting out high-carb foods, then either diet might be feasible for you. For keto, you must have access to high-fat foods for every meal.
Low-carb and keto diets can be difficult to stick to in the long run because they limit foods and nutrients. While the keto diet seems especially strict, it is important to note that you do not always have to be in nutritional ketosis while following a keto diet. There are people who have followed a keto diet for years or decades and do not always stay in ketosis.
In addition to difficulties with adherence, there are some potential harms of keto and low-carb diets. Either diet may put you at risk of inadequate nutrient intake, exacerbate conditions such as liver and kidney problems, and cause digestive issues from low fiber intake.
Additionally, carbs are necessary to provide fuel for physical activity, brain function, hormonal health, and much more. Even during ketosis, glucose can help prevent hypoglycemia, i.e. blood sugar levels being too low, and fuel tissues that can’t use ketones (e.g. red blood cells). Due to the potential challenges and harms of the two diets discussed, it is recommended to consult with a doctor and/or registered dietitian before starting a low-carb or keto diet.
- Cahill GF. Fuel metabolism in starvation. Annu Rev Nutr. 2006;26:1-22. doi:10.1146/annurev.nutr.26.061505.111258
- 2015-2020 Dietary Guidelines - health.gov. https://health.gov/dietaryguidelines/2015/guidelines/. Accessed July 29, 2019.
- Schutz Y. Protein turnover, ureagenesis and gluconeogenesis. Int J Vitam Nutr Res. 2011;81(2-3):101-107. doi:10.1024/0300-9831/a000064
- Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013;67(8):789-796. doi:10.1038/ejcn.2013.116
- Hussain TA, Mathew TC, Dashti AA, Asfar S, Al-Zaid N, Dashti HM. Effect of low-calorie versus low-carbohydrate ketogenic diet in type 2 diabetes. Nutrition. 2012;28(10):1016-1021. doi:10.1016/j.nut.2012.01.016
- Blagosklonny MV. The mystery of the ketogenic diet: benevolent pseudo-diabetes. Cell Cycle. 2019;18(18):2157-2163. doi:10.1080/15384101.2019.1644765