Obesity and sugar
Although we would like to eat as much as we want every day, the specter of obesity looms large. Today, this has become a serious issue facing society, associated with a host of medical conditions including high blood pressure and/or diabetes. Such symptoms are thought to be caused by poor lifestyle habits, from improper diets and insufficient daily exercise to excessive mental stress. Obesity is accordingly categorized as a lifestyle related disease. In 2023, 33% of men and 21% of women in Japan were diagnosed as obese (BMI over 25). In the USA, 42% and 21% of men and women respectively suffered the same condition, with extreme obesity affecting an additional 9% of men. In other words, more than half of American men are obese. Obesity places a burden not only on individuals but also society as a whole, due to the high medical costs it often entails.
We eat to support our energy needs. When our consumption exceeds those needs, (calories?) are stored as lipids in fat cells located in the liver, and/or under the skin. Recently, the results of biochemical research on obesity, especially in relation to sugars, are described in a book by Dr. Richard A. Johnson (Nature wants us to be fat. (2022) Kindle). Here, we provide a summary of what his interesting work can teach us about this growing problem.
At first, the author tells us that obesity is necessary for animals like bears to prepare for hibernation. During hibernation energy is sourced from stored lipids accumulated before winter through dietary consumption, especially fruits. Similarly, human obesity may partly be a self-defense mechanism, for example to protect women during pregnancy, when extra energy is needed to ensure sufficient nutrition for the growing fetus. Therefore, in some cases obesity is integrated into our physical systems as a survival strategy. This suggests that without careful daily maintenance of a healthy lifestyle, we may become easily obese. It should be noted that obesity may also weaken the immune system. It is well known that people with obesity suffer from Corona virus infection easily because of their compromised immune system. Needless to say, obesity is a condition to avoid if possible.
Our lives are powered by energy mainly from foods such as rice, bread and or noodles. These foods contain carbohydrates called glucose and starch, part of the sugar family. Such sugars are taken up into our cells through our intestine, then enter the bloodstream. Once inside cells, glucose is broken down through sequential biochemical reactions with various enzymes into carbon dioxide and water with oxygen. Through this process, the chemical energy stored in glucose is released and then easily trapped in a molecule, ATP. Energy stored in ATP is used for various physical functions like vision, protein synthesis, and activities in muscles, brain and other parts of our body.
Overeating results in excess ATP production which stops the function of an enzyme called iso-succinic acid dehydrogenase, leading to increased lipid synthesis. Consequently, succinic acid produced from glucose are not used to synthesize ATP but released from mitochondria into cytoplasm. There, the succinic acids trigger the production of fatty acids and then fat molecules. These fat molecules are stored in fat cells in the liver and/or under skin. When we “go on a diet”, these stored fats are degraded to make acetyl CoA, an intermediate metabolite involved in ATP production. Once in the mitochondria, it leads to increased production of ATP.
Dr. Johnson warns us to pay attention to excessive fructose consumption. Fructose is an extremely sweet disaccharide made of glucose and galactose. Fructose is added to artificial foods including drinks as a sweetener. This sugar is made from corn at an industrial scale as an additive of drinks and other foods. Therefore, high levels of this sugar are often consumed unconsciously, leading to obesity. However, eating reasonable amounts of fructose found in raw fruits is not harmful, but rather good for health.
Fig. Summary of Dr. Johnson’s book: Fructose and Obesity.
In Dr. Johnson’s book, he describes how fructose leads to obesity based on various scientific evidence. For example, he points out that fructose is degraded to release energy to make ATP, but the metabolic process is partly different from glucose. It is phosphorylated in cells by using ATP and this phosphorylated product is integrated into the same metabolic process as glucose. The first phosphorylation process consumes a lot of ATP producing ADP. This ADP leads to urinate production. Urinate inhibits ATP synthesis in mitochondria while also promoting succinic acid leading to higher fat levels.
Dr. Johnson’s book is a warning to us all to avoid becoming obese through excessive consumption of artificial fructose in processed foods. The solution he suggests is to avoid artificial foods and additives in order to evade the scourge of obesity and its associated lifestyle dependent diseases.