Normally, our bodies run on energy from glucose, which we get from food. We can’t store large amounts of glucose, however. We only have about a 24-hour supply. When a child has no food for 24 hours — which is the way the diet begins, usually in a hospital — he or she uses up all the stored glucose. With no more glucose to provide energy, the child’s body begins to burn stored fat.

The ketogenic diet keeps this process going. It forces the child’s body to burn fat round the clock by keeping calories low and making fat products the primary food that the child is getting. In fact, the diet gets most (80 percent) of its calories from fat. The rest comes from carbohydrates and protein. Each meal has about four times as much fat as protein or carbohydrate. The amounts of food and liquid at each meal have to be carefully worked out and weighed for each person.

Doctors don’t know precisely why a diet that mimics starvation by burning fat for energy should prevent seizures, although this is being studied. Nor do they know why the same diet works for some children and not for others.

Trying to put a child on the diet without medical guidance puts a child at risk of serious consequences. Every step of the ketogenic diet process must be managed by an experienced treatment team, usually based at a specialized medical center.

Often, a period of fine-tuning is needed before it’s clear whether or not a child is going to respond to the ketogenic diet. Doctors often ask parents to try the diet for at least one month, and even as long as two or three, if it’s not working at first.

A child on the diet usually continues taking anti-seizure medicine, but may be able to take less of it later on. If a child does very well, the doctor may slowly taper the medication with the goal of discontinuing it altogether.

About a third of children who try the ketogenic diet become seizure free, or almost seizure free. Another third improve but still have some seizures. The rest either do not respond at all or find it too hard to continue with the diet, either because of side effects or because they can’t tolerate the food.

A side benefit of the diet is that many parents say their children are more alert and make more progress when on the diet, even if seizures continue. If the diet seems to be helping, doctors will usually prescribe it for about two years. Then, they may suggest that parents slowly begin including regular food in the child’s diet to see if the seizures can still be controlled, even with a normal diet.

Sometimes a small amount of seizure medication is started again after the diet is stopped. However, some children may be able to stay seizure free without any further treatment. If the seizures return, the doctors may recommend putting the child back on the diet.

Like all the other treatments for epilepsy, the ketogenic diet has some side effects, which may or may not affect a particular child. Some side effects may go away if caught and managed early on. Knowing what to look for can make a big difference. Reported side effects include dehydration, constipation, and, sometimes, complications from kidney stones or gall stones.

Adult women on the diet may have menstrual irregularities. Pancreatitis (inflammation of the pancreas), decreased bone density and certain eye problems have also been reported. Again, this is why the medical team closely follows children or adults who are on the diet.

The diet lacks several important vitamins which have to be added through supplements. Sometimes high levels of fat build up in the blood, especially if a child has an inborn defect in his ability to process fat. This possibility can lead to serious effects, which is another reason for careful monitoring.

Most experts say the diet is worth trying when two or more medications have failed to control seizures, or when medications cause side effects that are having a harmful effect on a child’s life. It also helps to have a child who is willing to try foods that he might otherwise not be enthusiastic about, and is tolerant and not fussy about eating.

The diet seems to work for more than one kind of seizure, and for children who have a lot of seizures or few seizures. But most doctors say it shouldn’t be used instead of medications if the drugs are working and the child is not having bad side effects. Parents generally decide to try the diet because they hope it will give their child a better chance for a normal life.

However, the diet can be a barrier to some normal life experiences for children, especially those that revolve around food and holidays. And, like other treatments for epilepsy, it also can have side effects that affect some children more than others. So, as with any kind of treatment, there’s a lot to think about before deciding to try the diet.

Going over all the possibilities with your doctor is the best way to make the decision. It may also be helpful to talk with other parents whose children have been on the diet.

The diet starts in the hospital.

The child is placed on a 24-hour fast and is closely watched to be sure he or she is handling the very real stress of not getting any food during that time.

Once the child begins burning fat for energy instead of glucose (a state called ketosis), the doctors gradually introduce the foods that are part of the diet in amounts that are right for that child.

When the child goes home, the parents continue to carry out the diet at home, weighing every item and making sure that the balance between fat and other nutritional elements is maintained. Doctors and dietitians follow children closely to make sure they’re getting enough nutrition and are growing.

Parents of children on the diet use special paper strips to check the ketone level in the child’s urine.

Ketones are the chemicals that the body produces when it burns fat. Parents also test urine weekly for blood, which could be an early sign of kidney stones, a possible side effect of the diet.

When children (or adults) are treated with the ketogenic diet, the dietitian is a very important member of the medical treatment team.

The dietitian works out how much of one type of food or another should be served together to make the diet work. He or she helps the family plan the child’s meals, and works out how many calories the child needs for healthy growth.

Meal plans serve small amounts of fruits or vegetables (carbohydrates) and meat, fish or chicken (protein) with lots and lots of fat (such as cream, butter, eggs, or mayonnaise), and no sugar.

The following sample meal plans provide a general idea of the kinds of foods that are part of the diet.

Breakfast

• Scrambled eggs with butter
• Diluted cream
• Orange juice

Lunch

• Spaghetti squash with butter and Parmesan cheese
• Lettuce leaf with mayonnaise
• Orange diet soda mixed with whipped cream

Dinner

• Hot dog slices with sugar-free catsup
• Asparagus with butter
• Chopped lettuce with mayonnaise
• Sugar free vanilla cream Popsicle

These examples don’t show the exact amounts of each food because those have to be worked out for each child by the dietitian.

Each portion of food must be prepared very carefully by the parents, who often use a gram scale to weigh items exactly.

That’s because a tiny mistake in weighing and measuring foods (or if a child finds and eats a few cookie crumbs, or puts anything containing sugar — including medicines and toothpaste — in her mouth), can break the diet’s effects — and cause a seizure.