The liver produces all the glucose that your body needs, which is mostly used by the brain. The likely consequence is that you might need to eat more protein to replace the amino acids scavenged for this purpose.
In practice, you cannot contract a dietary deficiency disease from eliminating sugar unless you have a genetic defect affecting liver function. Even if you also eat no protein, your body will self-cannibalize muscle tissue to keep the brain alive.
It appears as though the evolutionary pressures on humans have produced support for two different energy metabolisms. In times of feast, where sugars and starches are consumed in excess, the body operates on glucose and glycogen, and stores fat. In times of famine, the body operates on ketones produced from its own body fat, and the brain operates on a combination of lactic acid and sugars scavenged from the body's protein stores.
The potential consequence of this is that if you ever do start eating significant quantities of sugar, your body will chemically signal that famine is over, and prioritize the restoration of your body fat stores. In other words, you can never go off the diet if you want to maintain your weight, as your body will want to turn every last scrap of excess sugar into fat as fast as possible.
This seriously sucks, because the brain is hardwired to love sweeter foods--foods that surround us constantly. It's like Lou Wu from Niven's Ringworld resisting the urge to eat the magic sweet potato that turns Pak breeders into protectors. Your limbic center wants that doughnut, no matter what that prudish frontal lobe says. So low-carb dieters have to consistently maintain a high level of sheer willpower for their entire lives. That may not be physically stressful in the cortisol-producing sense, but it is stressful mentally.
In practice, you cannot contract a dietary deficiency disease from eliminating sugar unless you have a genetic defect affecting liver function. Even if you also eat no protein, your body will self-cannibalize muscle tissue to keep the brain alive.
It appears as though the evolutionary pressures on humans have produced support for two different energy metabolisms. In times of feast, where sugars and starches are consumed in excess, the body operates on glucose and glycogen, and stores fat. In times of famine, the body operates on ketones produced from its own body fat, and the brain operates on a combination of lactic acid and sugars scavenged from the body's protein stores.
The potential consequence of this is that if you ever do start eating significant quantities of sugar, your body will chemically signal that famine is over, and prioritize the restoration of your body fat stores. In other words, you can never go off the diet if you want to maintain your weight, as your body will want to turn every last scrap of excess sugar into fat as fast as possible.
This seriously sucks, because the brain is hardwired to love sweeter foods--foods that surround us constantly. It's like Lou Wu from Niven's Ringworld resisting the urge to eat the magic sweet potato that turns Pak breeders into protectors. Your limbic center wants that doughnut, no matter what that prudish frontal lobe says. So low-carb dieters have to consistently maintain a high level of sheer willpower for their entire lives. That may not be physically stressful in the cortisol-producing sense, but it is stressful mentally.