The low-carb, high fat diet has been around for a while, both as a weight loss approach and a therapeutic approach to disease management. It has many names and forms, including the ketogenic diet, the Atkin’s diet, the Paleo Diet, and simply the “low carb” diet. I could go on and on about my ~feelings~ (by feelings I mean impassioned remarks based on my interpretations of science) about eliminating carbs from a diet, but I’ll focus specifically on the ketogenic diet for this post. Some of this gets pretty in depth with the science, so I’m bolding the most important concepts. Feel free to skim it!
Just to review, what foods have carbs?
Foods that contain carbohydrate include dairy (except butter, cheese has some carbohydrate but not much), grains, fruits, vegetables, and anything with sugar in it. Starchy vegetables like beans, potatoes, and corn contain much more carbohydrate than non-starchy vegetables like tomatoes, carrots, and broccoli. Plant protein foods like tofu and beans contain much more carbohydrate than animal protein foods like eggs and steak. Oils, lard, and butter contain virtually no carbohydrate.
So, what exactly is the “keto” diet?
The ketogenic diet is an eating pattern that is very low in carbohydrates, high in fat, and moderate in protein. The exact ratios of macronutrients are variable depending on the purpose of the diet. For adult general health or weight loss, the ketogenic diet generally consists of no more than 50 g/day carbohydrate, with higher amounts of fat and protein.1 For pediatric epilepsy management, the Pediatric Nutrition Care Manual from the Academy of Nutrition and Dietetics names the classic ketogenic diet as one that has a ratio of 4:1 or 3:1 grams of fat to grams of carbohydrate and protein combined.2 This is even more restrictive than the 50 g/day limit; a 2000 calorie diet would consist of 50-64 grams of carbohydrate and protein combined, with protein calculated according to patient needs and carbohydrate calculated from the difference. So, someone who needs 50 g protein per day would potentially only be able to eat 14 g carbohydrate with this form of the diet. The “keto” diet you likely here about on fitness blogs is the first version I described, whereas the 2nd version would be prescribed to a kid who is having a lot of seizures and medications aren’t working.
What’s the point??
The general goal of the ketogenic diet is to induce ketosis, or the production of ketone bodies that occurs naturally during starvation. Your body normally relies on glucose for energy because it is the most efficient. Your liver makes glucose from carbs and protein in your diet, as well as protein from your body’s muscles (and organs if you are really starving) and stored carbohydrate called glycogen. When there is no carb or extra protein around, your body uses fat to make these ketone bodies. The ketogenic diet tries to mimic starvation by limiting the carb and protein in your diet so that your body will use fat from your diet and your body to make ketones for energy. Your body won’t make ketones until it has used up all of its stored glycogen, because remember, it wants to use glucose for energy first.
The level of ketosis, or the amount of ketone bodies in the blood, depends on the amount of carbohydrate and protein consumed, and therefore the goal of the diet will dictate the specific ratio of macronutrients required. For example, weight loss may not require as high an amount of serum ketones as it would take to prevent seizures in a child. Even among children with epilepsy, a dietitian may need to adjust macronutrient levels to achieve the desirable level of ketosis, and the level of ketosis necessary to prevent seizures may differ as well.2
Does it work for epilepsy?
The ketogenic diet has been used to treat epilepsy since the 1920s. There is ample evidence showing that it can be effective for pediatric patients with difficult-to-treat epilepsy.3 It is unclear what biochemical mechanism makes this work, but there are theories that ketone bodies suppress neuron excitability, act as an anticonvulsant, or work via inhibiting the mTOR pathway.1 One study showed that only 10% of their pediatric epilepsy patients continuing the diet 6 years out. This is pretty understandable; can you imagine a kid being able to not eat goldfish for 6 years? However, clinical guidelines suggest as low as 2 years on the diet may lower the frequency of seizures permanently.4,5
Does it work for Type 2 Diabetes?
In Type 2 Diabetes, the ketogenic diet has been demonstrated to significantly improve blood glucose control and insulin sensitivity, even to the point of no longer needing medications.1 Logically, blood glucose control would occur because the lack of carbohydrate would mean your body won’t need to produce as much insulin as when you’re eating a balanced diet. Insulin sensitivity could be improved by decreasing serine phosphorylation of IRS-1 induced by hyperinsulinemia, allowing normal insulin signaling via tyrosine phosphorylation of IRS-1 to occur.6 These studies don’t discuss what kind of relationship patients have with food; you could achieve great blood glucose control and have a good relationship with food by spreading your carbs throughout the day, and using Intuitive Eating to learn how your body reacts to pairing carbs with certain foods.
Does it work for heart disease?
Ketogenic diets have also shown improvements in cardiovascular disease risk factors including lowering serum triglycerides and total cholesterol, increasing HDL (good cholesterol), and changing LDL cholesterol (bad cholesterol) to make it less harmful. It has been shown to increase the volume of LDL particles – smaller LDL particles have higher atherogenicity.1 A mechanism for improved lipid profiles could be that insulin normally activates HMG-CoA reductase; lowered insulin could lead to less HMG-CoA reductase activity, leading peripheral tissues to have lower intracellular levels of cholesterol and in response produce more LDL receptors, bringing in LDL from the blood. Similar to what I said above, you could achieve better cholesterol and have a great relationship with food by using Intuitive Eating principles to incorporate general lifestyle changes.
Does it work for weight loss?
I’ll preface this paragraph by stating that 95% of people who intentionally go on a weight loss diet gain all or more of the weight back within 5 years.7 Those that can keep the weight off do so using arguably disordered eating methods.8
Ok, let’s give the keto diet at least a chance…
There is evidence that the ketogenic diet can result in greater sustained weight loss at 1 year than a comparable low-calorie, low-fat diet.9 This has prompted researchers to theorize that the macronutrient distribution contributes to further weight loss beyond a simple caloric deficit in some way. Hypotheses for this include reduced appetite (greater satiety effect of protein, effect on appetite control hormones, possible appetite suppression from ketone bodies), reduction in lipogenesis and increased lipolysis, reduction in respiratory quotient and therefore more efficient metabolic use of fats, and an increased metabolic cost of gluconeogenesis.1 The metabolic efficiency/cost hypotheses are still not fully evidence-supported. The reduction in lipogenesis and increased lipolysis is definitely a viable hypothesis. In the short term, long chain fatty-acyl CoA, glucagon (high in this case because of low dietary carbohydrate), and AMPK inhibit ACC, producing less malonyl CoA, which inhibits CPT1 less and allows CPT1 to transfer fatty-acyl CoA into the mitochondria for beta-oxidation. This same process is upregulated in the long term by a high fat diet. Furthermore, beta-oxidation is promoted in the short term by a low insulin to glucagon ratio. In the long term, increased fatty acids bind PPAR-alpha and -delta which act as transcription factors, increasing the transcription of beta-oxidation enzymes. However, because the diet is high in fat, I am not entirely convinced that beta-oxidation of body fat is higher than beta-oxidation of dietary fat, resulting in a net loss of body fat mass. The hypothesis that ketone bodies and hormone changes suppress appetite seems like a much more viable reason that greater weight loss is seen with the ketogenic diet than other hypocaloric diets. But again, this diet has only been proven to show greater weight loss at 1 year than other diets, and just like any other diet, there is no evidence at all that it works long term for weight loss.
Cutting out carbs seems pretty restrictive…
Yes, it is quite restrictive. Depending on the individual, it is likely worthwhile for short term treatment in pediatric epilepsy management, and potentially short-term treatment for diabetes. However, restricting foods in any capacity puts individuals at risk for eating disorders and disordered eating. The extent to which the ketogenic diet limits carbohydrates results in a major restriction on fruits, vegetables, and whole grains, which are all significant sources of fiber and micronutrients. Furthermore, a ketogenic diet is so low in carbohydrates that glycogen stores would likely be low; this would make cardio exercise difficult. For any person that likes to do more cardio than simply walking around, this is not the way to eat. Equally as important is the fact that we also need to be able to enjoy all the foods our bodies can tolerate. Carbs taste good!! And most bodies are built to use them efficiently for energy. Many foods we enjoy in our culture as a part of normal social interactions and holiday gatherings are high in carbohydrates. Unless it’s deemed medically necessary, depriving yourself of carbs is not normal or healthy.
What’s the final consensus?
Overall, the ketogenic diet seems to work very well for kids with epilepsy, and potentially for diabetes and heart disease as well. Just like any other weight loss diet, it has not been proven effective in the long term. Unless it is medically necessary, and also depending on the individual person’s prior relationship with food, I would not recommend the ketogenic diet. It is not a balanced way to live and there are many other ways to promote health and well-being without cutting out entire food groups. Consider working with a Registered Dietitian that takes a Health at Every Size approach or is an Intuitive Eating Counselor to fine tune the nutrition that is right for you.
*I only discussed conditions for which the ketogenic diet has strong evidence. If you’d like to read more about emerging evidence for other conditions like PCOS and cancer, check out my first reference.*
Wishing you peace and happiness this holiday season ❤