Keto for Life? Reasons to Think Twice

Caroline Apovian, MD


February 06, 2023

Is the ketogenic diet the only way to lose weight? Of course not! Keep track of calories in vs calories out and almost anyone can lose weight. The problem is keeping it off. To understand that, we need to look at metabolic adaptation and the biology of obesity.

Our bodies have a "set point" that is epigenetically latched onto the environment the brain senses, just as the fetal environment responds to the maternal environment.

Caroline Apovian, MD

If food is plentiful, our hormones force us to eat until our bodies feel that there are enough fat stores to survive. Because of environmental influences such as highly processed food, preservatives, climate change, and regulation of temperature, our brains have decided that we need more adipose tissue than we did 50-100 years ago. It could be that an element in food has caused a dysfunction of the pathways that regulate our body weight, and most of us "defend" a higher body weight in this environment.

How to counteract that? Not easily. The ketogenic diet works temporarily just like any other diet where calorie intake is lower than usual. It seems to be agreeable to many people because they say they feel full after eating protein, fat, and perhaps some vegetables. Protein and fat are certainly more satiating than simple carbohydrates.

If strictly followed, a ketogenic diet will force the body to burn fat and go into ketosis. Without a source for glucose, the brain will burn ketones from fat stores. Owen and colleagues discovered this in 1969 when they did their now-famous studies of fasting in inpatients at Brigham and Women's hospital, using IV amino acids to protect muscle mass.

Keto for Life?

Is the ketogenic diet a healthy diet for the long term? That is a different question.

Of course not — we need high-fiber carbohydrate sources like whole grains, fruits, and vegetables to keep the colon healthy and obtain the vitamins and minerals needed to make the Krebs cycle, or citric acid cycle, work at its best.

Why, then, are we promoting ketogenic diets for those with obesity and type 2 diabetes? Ketogenic or low-carbohydrate diets are easy to teach and can rapidly help patients lose weight and return their blood glucose, blood pressure, and other metabolic parameters to normal.

 The patient will be instructed to avoid all highly processed foods. Studies have shown that highly processed foods, created to maximize flavor, "coerce" people to eat more calories than when presented with the same number of calories in unprocessed foods, a way to fool the brain.

Why Are We Fooling the Brain?

We circumvent the natural satiety mechanisms that start with the gut. When we eat, our gastric fundus and intestinal stretch receptors start the process that informs the hypothalamus about food intake. Highly processed foods are usually devoid of fiber and volume, and pack in the calories in small volumes so that the stretch receptors are not activated until more calories are ingested. The study mentioned above developed two ad lib diets with the same number of calories, sugar, fat, and carbohydrate content — one ultraprocessed and the other unprocessed.

That explanation is just the tip of the iceberg, because a lot more than primitive stretch receptors is informing the brain. There are gut hormones that are secreted before and after meals, such as ghrelin, glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and cholecystokinin (CCK), among a slew of others. These peptide hormones are all secreted from gut cells into the blood or vagus nerve, or both, and alert the brain that there is or is not enough food to maintain body weight at its set point.

It's a highly regulated and precise system that regulates body weight for survival of the species in this environment. However, the environment has changed over the past 100 years but our genetic makeup for survival of the fittest has not. The mechanism of action for defense of a higher body weight set point in this new environment has not been elucidated as yet. Most likely, there are many players or instigators involved, such as food-supply changes, sedentary lifestyle, ambient temperature, fetal programming, air quality, and global warming and climate change, to name a few.

The goal of obesity researchers is to investigate the underlying mechanisms of the increased prevalence of obesity over the past 100 years. The goal of obesity medicine specialists is to treat obesity in adults and children, and to prevent obesity as much as possible with lifestyle change and medications that have been shown to help "reverse" the metabolic adaptation to this environment. Our newest GLP-1/GIP receptor agonists have been shown in animal models to hit several pathways that lead to obesity. They are not just appetite suppressants. Yes, they do modulate appetite and satiety, but they also affect energy expenditure. The body's normal reaction to a lack of calorie intake is to reduce resting energy expenditure until body weight increases back to "set point levels." These agonists prevent that metabolic adaptation. That is why they are true agents that can treat obesity — the disease.

Back to the ketogenic diet. The ketogenic diet can fool the brain temporarily by using protein and fat to elicit satiety with less food intake in calories. After a while, however, gut hormones and other factors begin to counteract the weight loss with a reduction in resting energy and total energy expenditure, and other metabolic measures, to get the body back to a certain body weight set point.

The ketogenic diet also can help dieters avoid ultra- and highly processed foods. In the end, any type of diet that lowers caloric intake will work for weight loss, but it's the maintenance of that weight loss that makes a long-term difference, and that involves closing the metabolic gap that the body generates to defend fat mass. Understanding this pathophysiology will allow obesity medicine specialists to assist patients with obesity to lose weight and keep it off.

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