In the science community, few things have been debated as much as “carbohydrate vs. fat”. You can find dietitians on either end of the spectrum. Most functional medicine practitioners promote a more high-fat, lower carbohydrate lifestyle. On the other hand, medical organizations such as the American Heart Association and the American Diabetes Association argue the health benefits of a lower-fat, moderate-carbohydrate diet.
A lot of people have asked me about the ketogenic diet. In this ketogenic diet review, I will talk about the pros and cons in regards to weight management, chronic disease, and overall wellness. Keep in mind there are other researched uses for this diet (for epilepsy and other brain disorders), but I won’t be talking about those in this post.
Normally, our bodies use glucose (a sugar molecule) for energy. When the body does not have enough carbohydrates (or total calories) for energy, it releases fatty acids from the fat stores. The body then uses fat for energy instead. As a result of breaking down this fat, the body produces a compound called ketones. When our body uses ketones from fat for energy, this is known as ketosis. The level of carb restriction to induce ketosis seems to be individualized anywhere from 20-50 grams of net carbs per day. Note: dietary ketosis is NOT the same as ketoacidosis, which can occur in people with insulin-dependent diabetes and can be fatal if not treated.
The ketogenic diet highlights the “fat burning” effect of ketosis. To follow the ketogenic diet, you must rearrange how many macronutrients you eat to make fat your body’s primary fuel source.
There is a great deal of research about low-carbohydrate diets; however, the definition of “low carbohydrate” depends on however the researchers define it. So, interpreting the research about ketogenic diets, specifically, is difficult. Researchers report varying low-carb definitions from as low as 20 grams per day to up to 175 grams per day (<35% of daily calories for a 2000 calorie diet).
I always like dividing things into a pros and cons list. The ketogenic diet is very scientific, so I’ll do my best to break it down into “normal English”!
But, how do ketogenic diets help with weight loss? A few factors may come into play!
Satiety is a fancy word meaning fullness! Fat and protein keep us more satisfied (for longer) than carbohydrates. So, while you may be eating higher calorie foods on a low-carbohydrate diet (like avocado, butter, nuts, seeds, etc.) you may actually be consuming FEWER calories overall. When you aren’t as hungry during the day, you eat smaller portions and snack less (it seems obvious, but sometimes it’s not!).
In “traditional” diet-induced weight loss, our hunger hormone, ghrelin, increases, and our hormone that suppresses our appetite, leptin, decreases (4). This is part of the vicious weight loss cycle. We lose the weight, but as a result, our body attempts to counteract this process by revving up your appetite and hunger signals (I know, how rude!). However, some research shows that when the body is in ketosis, it actually mutes your hunger hormone. This all helps you to eat fewer calories each day (like the first point above).
Your body wants to take the “path of least resistance” to create energy. For example, it takes less effort for our body to use sugar as energy. When we force it to use fat as energy during ketosis, it has to work harder. Research thinks this is due to something called “reduced thermodynamic efficiency” (5). English, please? Your body has to use more calories to break down your meals when relying on a high-fat diet, which may help with weight loss.
While calories do matter in a sense, this last point makes us believe that there is definitely “more to the equation” than calories in vs. calories out!
One huge review analyzing over 50 studies and 68,000 people for at least one year concluded higher fat, low-carbohydrate dietary interventions led to a modest but significantly greater long-term weight loss than low-fat diets. The significance of this study was so large that the researchers even stated (6):
“Health and nutrition guidelines should cease recommending low-fat diets for weight loss given the clear lack of long-term efficacy over other similar intensity dietary interventions.”
The most popular argument against low-carbohydrate, high-fat diets is the potential long-term effects on heart health. In the 1970s, a scientist named Ancel Keys published the controversial Seven Countries Study. This study argued that people who live in countries with lower saturated fat in their diet have lower rates of heart disease. Keys, along with many major public health organizations, made the assumption that more dietary fat = higher cholesterol = higher risk of heart disease.
There are many things wrong with this study, and this generalized assumption. First of all, in the science community, we all know that correlation does NOT equal causation. In English: you can’t say something CAUSES something else just because there is a relationship. For example, ice cream sales go up in the summer. So do the rates of homicides. This doesn’t mean that ice cream causes people to commit murder.
Fortunately, we now know that fat, in general, does not cause heart disease (except for trans-fat which is no bueno). In fact, certain fats like those found in avocados, fish, olive oil, nuts, and seeds are actually protective against heart disease! We also know that high cholesterol foods actually do not significantly raise your cholesterol levels or risk of heart disease (4). We also know that while saturated fat may not be as healthy as monounsaturated fat, it does not cause heart disease (7, 8, 9, 10).
Studies show low-fat diets may lower LDL and total cholesterol; however, many of these low-fat studies show no effect (or a negative one) on HDL (the “good” cholesterol), triglyceride, and blood glucose levels (11).
The plot thickens. Large meta-analysis studies (basically analyzing a bunch of randomized controlled trials together) show that low carb, high-fat diets significantly improve cholesterol numbers more-so than low-fat diets.
The more likely culprit for heart disease and high cholesterol? Sugar!
In comparison to low-fat diets, higher-fat, lower-carb diets have been shown to significantly:
On the flip side, these same studies do indicate an increase in participants’ LDL cholesterol, which needs to be noted. One study showed that the ketogenic diet increased the SIZE and VOLUME of the LDL cholesterol particles (12). Instead of small, dense “bb” pellet LDLs, the particles were large and “fluffy”, which they argue actually decrease your heart disease risk. Experts have varying opinions on whether this increase in LDL poses an additional risk.
Because the ketogenic diet restricts carbohydrates, blood sugar levels will naturally decrease. The ketogenic diet has some preliminary research as a successful treatment for lowering hemoglobin a1c levels in people with type 2 diabetes (13, 14).
People on the low-carb keto diet generally have to eat less processed foods and sugars because of the carbohydrate restriction. We know that added sugar has been linked to many diseases like diabetes, heart disease, and cancer (15). So, I see this as a plus.
Very few studies look at the ketogenic diet as a long-term eating pattern. The longest study I found spanned 1-2 years in length. Does a lifelong keto diet have any adverse long-term health effects? We don’t know yet, because the research is so new. Which brings me to the next con of the keto diet…
Can someone eat low-carb keto for their whole life? Maybe. It wouldn’t be easy. The hunger lowering effect of ketosis only applies when your body remains in ketosis (3). The question is this: if you stopped eating a ketogenic diet, would your appetite hormones and cravings come back with a vengeance? Successful weight loss protocols deliver sustainable results that will help maintain the weight loss over time. A main concern with the ketogenic diet is the potential “yo-yo” effect oftentimes seen in the weight loss/weight regain battle.
The strict nature of the ketogenic diet also makes eating at social events and family gatherings more difficult. This can cause feelings of social isolation, and create an unhealthy obsession with keto “diet rules”. Extremely restrictive diets (for either fat or carbs) may lead to binge eating behaviors. If you have a history of disordered eating, a strict diet like keto is probably not the best fit for you.
The keto diet restricts some high-fiber foods like beans, fruit, and whole grains. Our bodies need at least 30 grams of fiber per day for optimal function. High-fiber diets have been linked to health benefits like lower rates of heart disease, decreased inflammation in the body, and a healthier microbiome (the good gut bugs) (16, 17). While it isn’t impossible to get enough fiber on the keto diet, it is definitely more difficult. Many people complain of constipation while on the keto diet because of this reason.
A keto dieter needs to include very large amounts of lower carbohydrate veggies to meet their fiber and vitamin requirements. Leafy greens, cruciferous vegetables (broccoli, cauliflower, Brussel’s sprouts), and avocados are a few examples. I’d have to assume that many people on the keto diet are not eating enough vegetables to meet their fiber or micronutrient needs. Ultimately, the fact that this diet restricts some vegetables that are higher in fiber is concerning to a veggie-loving dietitian like me.
Related Post: 5 Reasons to Eat Seasonally
The ketogenic diet shows promising research as a new medical nutrition therapy for conditions like high cholesterol, diabetes, and obesity (as well as epilepsy, but we aren’t discussing that one today). As far as long-term health and sustainability, the effects of the ketogenic diet are not well known. Professionally, I would not recommend a ketogenic diet, but do see the benefits for certain people as a shorter-term medical nutrition therapy. People may find the restrictive nature of the ketogenic diet difficult to maintain. Although, the keto diet does often have higher compliance rates than other low-fat diets (18).
Registered dietitians are the best health care providers to provide medical nutrition therapy. There are some nutrition pitfalls of the ketogenic diet (as described above), especially if carried out incorrectly. If you have one of these conditions and are interested in learning how it can help you, please reach out to a dietitian trained in ketogenic diets.
Disclaimer: please talk to your physician before starting or stopping any diet regimen.
Here’s the thing: the best diet for the general public is the one that doesn’t feel like a diet. I don’t recommend the ketogenic diet for the general public.
Any eating pattern that promotes real, wholesome foods, less processed ingredients, and cooking more from home will most likely better your health.
Fat is not the villain. I do not recommend a low-fat diet for the general public.
Include nutrient-dense sources of fat in your diet, with the majority sourced from mono and polyunsaturated fats. Saturated fat is not the devil (that’s another blog post in itself), but we shouldn’t be making it the majority of our diet, either.
Carbs are not “bad”. But, they shouldn’t be the focal point of our meals.
Stick to 1 serving, about 1/2 cup or a cupped hand, of carbohydrates when applicable. Choose complex sources of carbs, as tolerated, from sources like starchy vegetables, whole grains, fruit, and legumes.
Don’t obsess over your food.
Food is fuel, and food can be healing. But there is more to life than what we eat: family, friendships, memories, and experiences. It’s important to prioritize health in your life, but it’s also important to have a life.