Sugar Metabolism

Sugar metabolism is the process by which energy contained in the foods that we eat is made available as fuel for the body. The body’s cells can use glucose directly for energy, and most cells can also use fatty acids for energy. Glucose and fructose are metabolized differently, and when they are consumed in excess they may have different implications for health.

Looking at glucose first – when food is consumed, there is a corresponding rise and subsequent fall in blood glucose level, as glucose is absorbed from the gastrointestinal tract into the blood and then taken up into the cells in the body.

Glucose in the blood stimulates the pancreas to release insulin, which then triggers uptake of glucose by cells in the body (e.g. Muscle cells) causing blood glucose to return to base levels. Insulin will turn off fat burning and promote glucose burning as the body’s primary fuel source. Any excess glucose ends up being stored as glycogen in the muscles, and it can also be stored as lipid in the fat tissue.

Fructose is also taken up into the blood from the gut, but in this case, the liver serves as a pre-processing organ that can convert fructose to glucose or fat. The liver can release the glucose and fat into the blood or store it as glycogen or fat depots, which, if sugars are consumed in excess, may lead to fatty liver disease and also increase risk for diabetes and cardiovascular disease.

There are also some noted interaction effects between glucose and fructose, in that glucose enables fructose absorption from the gut, while fructose can accelerate glucose uptake and storage in the liver.

If the sugar comes with its inherent fibre (as with whole fruit) then up to 30% of this sugar will not be absorbed. Instead, it will be metabolized by the microbes in the gut, which may improve microbial diversity and help prevent disease. The fibre will also mean a slower rise in blood glucose, which has shown to have positive health effects.

It is easy to over-consume sugar

Concentrated Sugar Image

It is easy to over-consume sugar in juice and sweet drinks, as they contain mostly water and sugar. One glass of orange juice can contain concentrated sugar from five or six whole oranges. And while it is easy to drink that much sugar, you would be less likely to eat that many oranges in one go.

Fizzy drinks do not make you feel full as quickly as foods do. This makes them easy to over-consume. And a small fizzy drink contains nine teaspoons of added sugar, so drinking just one can means that you have almost reached your recommended maximum intake for that whole day.

When we eat something that contains carbohydrate (sugar), it is broken down into smaller glucose molecules and this signals the pancreas to release the hormone insulin. Insulin must attach to the insulin receptor on the cell to allow the glucose to pass through the cell membrane. Once inside the cell, the glucose proceeds to the mitochondria where it is converted to the energy molecule adenosine tri-phosphate (ATP). This is the molecule used by the entire body for its source of energy.

But what happens when we go for long periods of time without food? Our bodies are only able to store enough glucose in the liver to last about 48 hours. After that it begins to convert muscle into glucose. This process can last for up to 40 days but after about two weeks we would consume so much muscle that survival would no longer be possible.

What happens is that the body begins to use its store of fat for fuel. Triglycerides are the storage form of fats. These are converted into fatty acids and then into what is known as ketone bodies (molecules). Ketones can be used as fuel for the cells, replacing glucose, and have the further advantage that they do not need insulin to pass through the cell membranes. Ketones can be used by the brain, the heart and the muscles and help people stay alive during periods of starvation.

The tremendous advantage of using ketones over glucose as fuel for the body is they bypass the need for insulin and restore blood glucose to healthy low levels without overtaxing the pancreas!

As we fast overnight when sleeping, a small amount of ketones are made, but as soon as we eat a typical breakfast, they disappear. If we continue to fast for two or more days, the levels of ketones are increased significantly.

Ketones can be produced in the body by exercise and diet. The Ketone Diet is the most fascinating area of nutritional research being conducted in medicine today.* It has therapeutic possibilities in a wide variety of neurological diseases, including Alzheimer’s disease, epilepsy, headache, Parkinson’s disease, brain cancer, autism and multiple sclerosis. (3)

As Dr. Newport points out in her book, Alzheimer’s disease is increasing becoming known as a metabolic condition of poor sugar metabolism in the brain. Insulin is needed in the brain to allow glucose to cross into the cells to produce ATP. However insulin cannot cross the blood-brain barrier to get into the brain.

Until 2005, it was commonly thought that insulin was only produced in the pancreas. Then it was discovered that the brain makes its own insulin. A new body of thought is developing that insulin resistance or a deficiency of insulin in the brain are responsible for cognitive impairment and Alzheimer’s disease. Researchers are now commonly referring to Alzheimer’s as “type 3 diabetes.” As such, the Ketone Diet is a promising therapy to reduce insulin resistance in the brain and prevent deterioration from the disease.

Dr. Dominic D’Agostino is a leading researcher into the uses of the Ketone Diet for disease conditions. He discusses how all cells are fueled by glucose. When glucose is not available, the cells have the ability to switch over to the alternate fuel, ketones. Except for cancer cells. They have a defect that does not allow them to shift over. So, by using the Ketone Diet, cancer cells are selectively starved and die. “It just absolutely amazes me that medical science is just now finding this out,” he said. (4)

And, to get back to the origins of this article, a Ketone Diet has been shown to be effective in improving sugar metabolism and reducing the need for medications in patients with type 2 diabetes. (5)

Ketone Diet Restrictions

The pure Ketone Diet is very restrictive and difficult to follow. It mandates that 80% of calories must come from healthy, medium chain fatty acids, such as those found in coconut oil and palm kernel oil. Only 20% of calories can come from combined carbohydrates and protein. This diet will lead to a dramatic increase in ketone bodies and a decrease in glucose and insulin.

When a person eats foods that contain medium chain fatty acids, they are absorbed from the small intestine and transported directly to the liver, where they are partially converted to ketones and released into the bloodstream.

The oils normally consumed in the US, such as soybean, olive, canola, corn, peanut and sesame, do not contain any medium chain fatty acids. 

A word about ketosis: When doctors worry about the possible dangers of raising ketone levels, they are thinking about diabetic ketoacidosis, a potentially life threatening condition that happens to some people with type 1 diabetes. The levels of ketones become dangerously high, as much as 5 to 10 times higher than the situation of starvation or the classic Ketone Diet. The levels of ketones are 50 times higher in diabetic ketoacidosis than after consuming a large quantity (20 grams) of medium chain triglyceride (MCT) oil.

2 – Mary Newport, MD. “Alzheimer’s Disease: What if There Was a Cure? The Story of Ketones.” Copyright 2011. Basic Health Publications, Inc. Laguna Beach, CA

3 – Stafstrom CE, Rho JM. “The Ketogenic Diet as a Treatment Paradigm for Divers Neurological Disorders.” Front Pharmacol. 2012, 3:59.

4 – Friday, June 21, 2013.

5 – Yancy YS Jr, Foy M, et. al. “A low-carbohydrate, ketogenic diet to treat type 2 diabetes.” Nutr. Metab. (Lond). 2005; 2:34.

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