I get this question so often I feel like a broken record, so I'm finally putting all my recommendations down in one spot for all to read! This is not just my opinion...this is science.
Short answer: Probably not.
Long answer: It depends.
The majority of the population, however, likely does not need to be on, nor do most people function optimally on, a ketogenic (keto) diet. It was originally used to help those with epilepsy control seizures. It is essentially nutritional starvation, not always a health-promoting lifestyle change. That being said, there are specific situations in which people may benefit from a ketogenic diet, which you can read more about here.
Why don't I recommend this diet for most people?
Metabolic Function
Carbohydrates are necessary for producing thyroid hormone. There is a thyroid receptor on every single cell in the human body. The thyroid is necessary for proper metabolic and overall organ function. If the thyroid is not fueled properly, the entire body doesn't function correctly either. Because thyroid function is necessary for metabolic function, this means that if the thyroid doesn't function properly 1) our bodies don't digest food correctly and 2) our metabolism slows down in general...and who wants a slow metabolism?
" 'Studies show that cutting too many carbohydrates can decrease thyroid function and increase stress hormones, making it harder to burn fat and lose weight...a multi-center study published in JAMA found that extreme carb restriction lowered participants' thyroid hormone levels by 22% within four weeks while upping levels of the fat-storing stress hormone cortisol by 21%.' " -Sara Gottfried, M.D., First for women
Digestion
In addition to improper digestion and metabolism, there is also a very basic reason the keto diet is not super for digestion...it lacks fiber, which is extremely vital to human health. Some people may be able to achieve ketosis eating fiber-filled fats and low-sugar vegetables, however, not everyone approaches it this way. I see many diets consisting of increased amounts of bacon, butter, cream, cheese, meat, etc., which are not unhealthy foods when eaten in moderation, but they do lack fiber. Too many of these foods are not conducive to cultivating a healthy gut microbiome. Our gut bacteria thrive on pre-biotic foods containing soluble and insoluble fiber, resistant starch, and certain types of proteins and fats. Some of the best sources of pre-biotics include vegetables of all kinds, berries, apples, oats, cold potatoes, cold rice, green bananas, beans, legumes, fish, olive oil, and dark chocolate. Some of these foods are either limited or not allowed when sticking to 50g or less of carbohydrates each day.
Additionally, saturated fat is 1) not great for gut bacteria and 2) requires our bodies to produce more insulin to deal with any carbohydrates eaten along with it.
All this to say, the keto diet can increase risk of many health issues related to lack of good bacteria in the gut, but a main one is constipation due to lack of fiber/bulk in the stool. The opposite, diarrhea, can also occur due to high fat/oil consumption and a lack of binding/bulking soluble fiber.
Furthermore, fat digestion is hard on the body! The process is long and requires a bit more effort from our bodies; enter: bile. Fats are the only macronutrient that require bile for complete digestion and breakdown, and if people have any gall bladder issues (the organ that produces bile), they will know. They will be in pain when they try to eat a high fat diet because those fats will go undigested.
Insulin Resistance
Often times the keto diet is used to balance blood sugars, which has been helpful for many people. But what happens when they start eating carbohydrates again? Now their bodies aren't used to dealing with much glucose, which can lead to further insulin resistance. And remember what I said about saturated fat and increased need for insulin, a nutrient that is often highly consumed when following a ketogenic diet? Besides that, insulin resistance isn't just about sugar...it's also about inflammation. Without addressing the inflammation, insulin resistance may still be a problem. And yes, eliminating processed sugars/carbs will definitely, in part, heal much of that inflammation, however, limiting whole food carbohydrates is not always necessary and many have anti-inflammatory compounds (beets, sweet potatoes, berries, green apples, etc.).
Brain Health
Allowing our bodies to utilize ketones has been said to induce higher brain function. First, however, this doesn't happen for everyone. Some experience brain fog because glucose is the brain's preferred fuel source. Second, when we enter ketosis, we enter nutritional starvation. During normal starvation (not eating/not eating enough), our bodies can eventually enter ketosis, at which point our bodies and brains do gain a heightened awareness. Why? Because it's starving and trying to find food. Without this safety mechanism in place, our bodies would be more likely to die than to find food and survive. This heightened function, however, is also not always complete. When we are on a fasting high, we are happy and enlightened, and can perform physical activity, but some level of brain function, like holding conversations, focusing, etc., can actually become more difficult. Again, however, this is not the same for everyone.
Nutrient Deficiency
Any kind of elimination diet runs the risk of nutrient deficiency. That's mainly why elimination diets aren't meant to last forever. The keto diet limits entire food groups, which limits a wide range of vitamins and minerals. If you are on a keto diet, I highly suggest a multivitamin and being very mindful of nutrient density. Additionally, because a keto diet can cause metabolic and digestive dysfunction, food potentially isn't being broken down enough once it hits the small intestine, where vitamins and minerals are absorbed. How can you tell? Check your poop! If there's undigested food in there, it wasn't digested and nutrients weren't absorbed by the body.
Energy Levels
Low energy levels often result from a keto diet---and not necessarily because people didn't follow it correctly. Some people, especially women, just do not run as well on ketones as others because for most of us, glucose is the preferred fuel source. The body runs on both fuel sources, not just one or the other. It is not as if if your aren't in ketosis your body is only burning glucose and will never tap into fat stores--it will burn both sugar and fat on a regular diet. Some organs use fats better, while some use glucose. The intensity of activity changes which type of fuel burned as well. At low intensities, the body burns more fats and at high intensities, muscles demand more glucose. I will say, the heart does run better on ketones, but as for the brain and muscles, glucose is generally best, especially if you are trying to do higher intense activity. So, on top of low energy levels, lack of glucose can also lead to muscle breakdown. Why? glucose is used to build, and is stored in, the muscles. Our bodies generally need carbohydrates to build and maintain muscle mass, as well as fuel muscle function. Muscles can often feel weak and sore without enough glucose.
And numerous other reasons you can read more about here:
http://perfecthealthdiet.com/2011/08/carbohydrates-and-the-thyroid/
https://nutritionstripped.com/what-is-ketogenic-diet/
https://www.thepaleomom.com/adverse-reactions-to-ketogenic-diets-caution-advised/
Additionally, fats are not bad! They are a necessary part of the human diet and needed for overall body function, but there is a HUGE difference between including plenty of healthy fats in the diet and consuming 70-75% of calories from fat in the diet, while limiting other macronutrients.
Carbohydrates aren't bad either! Whole food carbohydrates are a necessary macronutrient that contain a wide variety of fiber, vitamins, minerals, and blood-sugar balancing compounds.
Point being: Eat a balanced diet of whole foods and you'll be more likely to gain health and still lose weight (if that's the goal) and obtain all the nutrients you need. The keto diet isn't the only answer.
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