Dr. Nathan Lanning, cellular and molecular biologist and a member of Hope Protestant Reformed Church, Redlands, California.

All things are lawful unto me, but all things are not expedient: all things are lawful for me, but I will not be brought under the power of any. I Corinthians 6:12

In order to remain alive and properly function, the cells that make up our bodies must continually take in nutrients. These nutrients provide the raw materials required for the production of hormones by endocrine cells, by digestive enzymes, by intestinal cells, by hemoglobin in red blood cells, and by the myriad of other items produced by our dozens of additional unique cell types. Nutrients also provide our cells with a critically important energy source to power all of our body’s functions.

The nutrients that are converted to cellular energy come in many forms, some of which are considered ‘healthier’ than others. In part, it is for this reason that the nutritional contents of foods are required to be displayed on most items in the grocery store. Most of the nutritional contents that we find in the grocery store are just fine for consumption by the average healthy individual, but only in appropriate (or balanced) doses. Therefore, it is wise for us to maintain some level of awareness with respect to the nutritional content that we consume. We must eat in order to remain alive. However, our gracious God has given us the gift of being able to enjoy eating food. Many of the nutrients that God has seen fit to include in the creation are undeniably delicious, and we can praise Him by partaking of these nutrients with thanksgiving and to His glory.

As I write this, the holidays are rapidly approaching, and I anticipate enjoying the delightful culinary creations associated with this time of the year. However, uninhibited consumption of holiday delicacies or “everyday” foods is not wise for two reasons: Scripture urges moderation in all things and overconsumption of certain nutrients can lead to poor health. Remarkably, the distinct physiological processes that lead to poor health from overconsumption of some nutrients have been identified. It is interesting to consider how the Creator governs these processes so that it truly does become wise to observe moderation in this context from an earthly human-health point of view.

In fact, our cells can harvest energy from many types of nutrients; however, the most common nutrients associated with providing cellular energy are carbohydrates. There are three major types of carbohydrate content in most foods available from the grocery store: starch (naturally found in wheat, corn, potatoes, and rice); sucrose (naturally found in many plants and fruits, but also refined from these sources and used as an additive sweetener); and high fructose corn syrup (HFCS, purely an additive sweetener). Starch is made up of long chains of the molecule glucose (hundreds to thousands of glucose molecules linked together), while sucrose is made up of only two individual molecules bonded together: glucose and fructose. HFCS is a mixture of individual glucose and fructose molecules. Our cells can only harvest energy from these carbohydrates when they are present as individual molecules; therefore, when we consume starch, enzymes in our saliva and small intestine break starch into individual glucose molecules, and enzymes in our small intestine break sucrose into individual glucose and fructose molecules. Glucose and fructose are also naturally found as individual molecules in most fruits.

Individual glucose and fructose molecules (also called simple sugars) are absorbed into our blood from the small intestine, and then transported to our liver, which serves as our body’s command center for distributing sugar through the blood stream to cells in need of energy. This function of the liver is readily accomplished with glucose, which is alternately stored in the liver or sent throughout the body when energy is required. However, the same is not true for fructose. In fact, diets high in fructose (diets high in sucrose or HFCS) pose two challenges to the liver with respect to regulating sugar levels in the body.

The first challenge is related to the amount of glucose and fructose that liver cells extract from blood as it passes through the organ. Liver cells extract a relatively small percentage of the total glucose out of the blood, allowing the majority of glucose to pass through the liver and on to the rest of the body. However, liver cells extract nearly all of the fructose from the blood as it passes through, leaving almost no fructose to be distributed to other cells and tissues. Therefore, foods high in sucrose only deliver half of the sugar molecules to “energy hungry” tissues such as brain and muscle (again, sucrose is broken into one glucose and one fructose molecule). In order to supply your muscles and brain with the same amount of energy, you would have to consume two times the amount of sucrose as starch—and you would have to consume even more than that for some HFCS foods that contain an even greater proportion of fructose compared to glucose.

This is the challenge posed by diets high in fructose: the brain receives information that a meal with high sugar content has been consumed but it does not receive much energy from that meal. Therefore, when individuals make high fructose-content food a regular and significant part of their diet, a disconnect can develop between the brain’s ability to assess the amount of energy consumed and the actual amount of energy available to the entire body in their food. This is important because the brain is extremely reliant on energy from sugar and sends out signals to meet its energy needs. If the brain senses that the body is regularly consuming high sugar content but is not receiving much energy from those foods, it can raise the threshold for how much sugar content must be consumed to meet its needs. Practically, this can result in individuals desiring to eat lots of food with very high sugar content but with no associated feeling of satisfaction. This situation can adversely affect the health of these individuals due to the second challenge related to fructose and the liver.

The second challenge deals with the actual energy-harvesting process that occurs within cells. This process consists of a series of chemical reactions (metabolism) which transfer the energy in the sugar molecules into a different molecule, yielding energy in a form that cells can use. The chemical reactions of glucose metabolism include something analogous to a safety switch or circuit breaker that is triggered when energy production reaches a sufficient level. When this happens, glucose metabolism is halted and the remaining glucose is converted into the carbohydrate, glycogen, and stored or sent back out of the cell. Fructose metabolism in the liver, however, does not trigger this safety switch. Instead, fructose metabolism bypasses the safety switch and continues unceasingly to convert fructose into fat molecules in the liver. Therefore, liver cells essentially clean out all of the fructose content from food, convert it to fat, and do not make it available as energy for the rest of the body. These fat molecules can accumulate in the liver, disrupting normal liver function, and can also be distributed through the blood stream to the rest of the body, causing additional adverse effects. Recent research has shown that persistently high sugar intake levels trigger numerous other undesirable cellular reactions in addition to the production of fat molecules, leading to additional health considerations.

The rise of obesity, fatty liver disease, and metabolic disease show strong correlations with the rise of sucrose and HFCS as an additive sweetener in the Western world. Therefore, the medical and scientific communities have been intensely scrutinizing the possibility that overconsumption of fructose is a contributing factor to these diseases. While there has been healthy debate between opposing viewpoints over the years stemming from inconclusive data, the most recent studies strongly suggest that high levels of fructose in our nutritional content can and does contribute to these diseases. While fructose is a completely natural sugar, consuming it in large quantities (such as in foods and drinks containing lots of sucrose or HFCS) likely has detrimental health consequences.

Perhaps all of these physiological details are not necessary for us to follow the advice of medical associations, physicians, and health-conscious mothers on this topic: be aware of the nutritional content that we consume, and make an effort to consume balanced diets. Scriptural wisdom advising moderation (I Cor. 6:12, Gal. 5:22-23) with respect to wine (Eph. 5:18, Prov. 20:1), sleep (Prov. 23:20-21), and even honey (Prov. 25:16, 27) can certainly be applied to our general diet awareness, and our current understanding of fructose and liver physiology can also be taken into account when making these applications. I admit that I have the proverbial “sweet tooth” and should spend more time meditating on these passages in light of these facts. The sweetness of fructose is a good gift to us—thanks be to the Creator as we wisely use it with thanks, to the praise of His name.