What if ketosis isn't the altered state?

Most discussions of metabolism begin with carbohydrates already in the picture. 

We eat, glucose rises, insulin responds, glycogen is replenished and the brain uses plenty of glucose. That becomes normal. Take carbohydrates away and suddenly the body is described as changing. Glycogen drops, fat burning increases, ketones rise and the liver makes more glucose. We call someone “keto adapted” or “fat adapted,” as though the body has entered an unusual condition.

Start from the other direction.

Take someone who has eaten very little carbohydrate for months. Fat supplies most of the body's energy, the liver makes the glucose still required, and the brain uses ketones extensively. Now feed that person carbohydrate. Blood glucose and insulin rise. Ketone production falls. Release of stored fat slows. Glycogen and its associated water increase. We don't describe this as the altered state because carbohydrate eating is where we started.

Even the statement that the brain “needs carbohydrates” looks different from there. The brain needs some glucose, but we don't have to eat carbohydrate to provide it. The body can make glucose while ketones provide much of the brain's energy. Dietary carbohydrate and physiological glucose are not the same requirement.

Carnivore diets make this hard to ignore. People live for long periods with almost no dietary carbohydrate while continuing to think, work and exercise. Many report steadier appetite and fewer meals. That doesn't make fruit or vegetables harmful. It shows how far human metabolism can travel in the other direction.

I've noticed something similar with fasting. If I haven't fasted for a while, the first few attempts can be miserable. Hunger feels urgent and food keeps coming to mind. After I've done it several times, that changes. I can go much longer without eating and barely notice it.

More surprising, I often become less hungry the longer I fast.

If hunger simply measured how badly the body needed more calories, that would make little sense. Five hours without food should feel worse than three, and ten worse than five. Instead, hunger comes and goes. As access to stored fat increases and ketone production rises, food can become less important.

The calories did not suddenly appear. Access to them changed.

That miserable first fast may tell us more about the transition than the state on the other side. The same can happen when carbohydrates are sharply reduced. Feeling lousy during the first few days tells us about changing fuel sources, not what that metabolism will feel like weeks later.

This makes metabolic flexibility more interesting than arguing over whether glucose or fat is the better fuel. We have both systems. We can eat carbohydrate, raise insulin and store energy. When food disappears, insulin can fall, stored fat becomes more available and ketone production can increase.

The trip matters in both directions. Someone who cannot comfortably go without carbohydrate may have poor metabolic flexibility. So may someone who lives in ketosis but handles carbohydrate badly when it returns.

Modern eating gives us little reason to make that trip often. Breakfast comes soon after waking. Lunch follows a few hours later, with snacks often filling the space. Dinner comes, perhaps something afterward, and another breakfast is never far away. Food is always available, so the body rarely moves deeply into stored fuel before more energy arrives.

That may matter as much as how many carbohydrates are on the plate. Our metabolism can move between incoming glucose and stored energy, yet modern eating can keep us close to one side almost all day.

We accept this kind of adaptation elsewhere. Exercise becomes easier with practice. Heat, cold and physical exertion call on capacities that improve with use. Fasting is unusual mostly because our food supply is so dependable that we can avoid the challenge almost completely.

We often judge health by how comfortable the body is when everything it expects is continuously supplied. It is also worth noticing what happens when those conditions change.

The next meal comes. Glucose rises, insulin responds, ketones fall, and the body moves back. Perhaps health is not one perfectly maintained metabolic state. Perhaps health includes the ability to change states.

Seth Schneider is a health columnist for the Bonner County Daily Bee.