Everyone experiences peaks and troughs in energy throughout the day. Some of this is natural — governed by our body’s internal circadian rhythms. Our energy levels during certain times of the day are also influenced by our chronotype (are you an early bird or a night owl?) and routines that we’ve established over the years.
But what we do, and perhaps more importantly what we eat, can directly impact our energy levels by influencing our glucose levels. Since glucose is one of our body’s main sources of energy, glucose levels have a major impact on our overall energy, mood, and performance.
Glucose is a simple carbohydrate (simple sugar) that is the primary energy source for most of our body’s cells. Blood glucose simply refers to the concentration of glucose that’s circulating in our blood — which is how it’s transported to tissues that need it for energy.
Speaking of energy, glucose is the primary energy source for our brain, which needs a constant supply of glucose because — unlike our muscles — the brain can’t store glucose nor can it use fatty acids. Glucose is also a primary fuel source for skeletal muscle, especially during exercise.
At any one time, we’ve got about 4 grams of total glucose in our blood — about one teaspoon. But when we talk about blood glucose, we usually refer to the concentration of glucose in the blood, which ranges from 70-100 mg/dL in a non-diabetic person. When we eat a meal, blood glucose will typically rise, and the level that it rises will depend on the content of the meal. In any case, a “healthy” rise in glucose of up to 140 mg/dL might be expected after eating. Anything above this could be considered an abnormally large glucose spike.
Along with our blood glucose, we can also store glucose as glycogen in our liver and skeletal muscles. We store about 100 grams and 400 grams of glycogen in the liver and muscles, respectively.
There’s been a steep spike (pun intended) in the interest in blood glucose among health aficionados. Why is glucose an important or worthwhile metric when it comes to optimizing our energy?
For one, blood glucose is easy to measure using one of several commercial devices, and now you can even purchase a continuous glucose monitor (CGM) that allows you to see your glucose levels throughout the day.
There is some “debate” as to what the ideal average level of glucose is. In reality, fasting glucose is going to vary from one person to the next. Knowing your average numbers is a good way to assess your risk for disease and determine whether you need to make modifications to your diet or exercise regimen.
But a single measure of fasting glucose may not be the most important thing when it comes to your daily energy levels. As we’ve discussed, blood glucose levels can and will fluctuate throughout the day — rising after meals and during exercise, and falling during other times. This is a concept known as glucose variability, and it has a profound effect on our energy fluctuations throughout the day.
Glucose variability refers to the fluctuations (rises and falls) of our blood glucose throughout the day. If you look at a “normal” blood sugar profile throughout someone’s day, there will typically be noticeable spikes in glucose, as well as times when glucose falls back to baseline or sometimes below. These rises will sometimes be associated with meals, although glucose also typically rises after we wake up and in response to exercise.
Blood glucose levels also undergo a normal rhythmic rise and fall at certain points during the day due to our circadian rhythms of glucose and insulin release. In other words, rising and falling blood glucose is a normal phenomenon.
It’s not the variability in glucose levels that can cause the energy “rollercoaster” we all want to avoid, but rather, a large magnitude of variability. Large rises in glucose followed by steep troughs (which occur due to our body’s overproduction of insulin, the hormone that lowers blood glucose) are associated with fluctuations in mental and physical energy — in addition to numerous other adverse health outcomes. Increases in glucose may temporarily provide a quick hit of energy, but too steep of a rise may lead to anxiety or an inability to focus.
It might seem odd that we want to avoid large glucose spikes, given the common (mis)perception that a “sugar rush” is a period of heightened energy. One study concluded that carbohydrate consumption may actually increase fatigue and negatively impact mood within an hour of consumption. Of course, this will depend on the type of carbohydrates consumed, the number of carbohydrates, and one’s individual carbohydrate tolerance. So while glucose is indeed a source of energy, flooding our body with too much of it at once appears to take away from energy, rather than contribute to it.
The consequent large drop in glucose after a spike will then cause you to feel lethargic, moody, and unfocused. Many people ride these energy tidal waves all day long.
A rapid change in the amount of energy provided to our cells is not a great way to sustain mental focus and performance throughout the day. Glycemic variability is intricately linked to our brain function and therefore, plays a key role in our energy. Maintaining energy homeostasis appears to rely extensively on our ability to regulate glucose levels within a normal range and avoid high glucose variability. Again, the brain plays a critical role here and seems to perform best when glucose levels are somewhat stable.
Our brain is the primary sensor of glucose levels in the body — responding to changes in glucose by controlling whole-body energy production and metabolism. The glucose-sensing capabilities of the brain ensure that our body’s energy production is sufficient to meet the brain’s high metabolic demands — which are about 20% of the body’s total energy requirements and almost 50% of the body’s glucose requirements.
Frequent spikes and dips in glucose — especially large ones — challenge the brain’s ability to regulate energy production. In addition, high glucose variability stresses the sympathetic nervous system, which also plays a key role in energy production. On the other hand, less variable glucose levels that are characteristic of a healthy metabolism provide sustained energy to the brain and body.
Because glycemic variability is harder to measure and is a relatively “newer” concept, not much research has been done on how it impacts energy levels. However, glycemic variability has been linked to central nervous system (CNS) oxidative stress and inflammation., with implications for brain energy production and the development of cognitive decline. High glycemic variability may contribute to a feeling of “brain fog.”
For high energy, chase a low glucose variability during your day.
Hyperglycemia (high blood glucose) is defined as a fasting blood glucose greater than 125 mg/dL or post-meal blood glucose levels greater than 180 mg/dL — although more strict advocates of glucose control would suggest that 140 mg/dL represents a healthier threshold.
It is important to remember that glucose levels can rise after eating a meal, but an abnormally large rise in glucose is something to be avoided. When glucose rises too high, some people can experience jitters, anxiety, a rapid heartbeat, and have a hard time focusing on work and other tasks. Giving the brain more glucose doesn’t mean we will experience more energy, and sometimes, the contrary may be true.
Frequent periods of high blood glucose can place stress on the brain and energy production. Furthermore, hyperglycemia has been shown to reduce the body’s ability to produce ATP and the function of our mitochondria by contributing to inflammation and oxidative stress.
But glucose is also necessary for optimal mental energy and performance, and in the absence of hyperglycemia, glucose helps to improve attention and memory. Challenging mental (and physical) tasks require us to use a lot of glucose, and providing the body with the energy to perform is important. Consuming glucose can increase energy levels in the brain and improve cognitive performance and memory.
Consuming carbohydrates — and by proxy elevating blood glucose — is also well-evidenced to improve physical energy and high-intensity exercise performance.
From this, we can conclude that abnormally high blood glucose, otherwise known as hyperglycemia, seems to reduce energy in the short term. The “sugar rush” is no way to achieve peak energy levels, nor does the research suggest that a “sugar rush” even corresponds to a short-term increase in energy.
However, maintaining stable blood glucose levels, with normal moderate rises in response to meals and other daily events, is essential for maintaining our energy levels. Small increases in glucose likely provide us with energy and help supply fuel for the brain and the body.
Just as there are energetic risks of letting glucose get too high, letting glucose dip too low can also adversely affect our energy levels. A blood glucose level that is too low (usually defined as under 70 mg/dL) is called hypoglycemia. Though this condition occurs frequently in people with diabetes, it can occasionally happen in non-diabetic people. The main reason for a short-term drop in blood glucose is the “rebound” from eating a high-carbohydrate meal, especially one high in refined carbohydrates and low in fat and protein. A sharp rise in blood glucose will cause a subsequent rise in insulin, which works to bring glucose levels back down to normal. But too much insulin released too quickly can cause hypoglycemia.
Hypoglycemia is a situation where the brain is deprived of energy, and this affects energy levels throughout the body. Worsened vision, confusion, lethargy, shakiness, sweating, and trouble concentrating are all symptoms of hypoglycemia. Mood changes are also common during an episode of low blood glucose.
A lot of the research on hypoglycemia has been conducted in people with diabetes. But hypoglycemia significantly impairs brain metabolism, and even short-term reductions in blood glucose decrease simple brain functions and the activation of several brain areas while performing certain cognitive tasks.
Though hypoglycemia may be rare among people with normal glucose metabolism, we can all experience dips in blood glucose that impact our energy levels throughout the day. Even milder drops in glucose can leave us with a feeling of brain fog, fatigue, and a lack of motivation. Low glucose can also significantly reduce strength and endurance since our bodies won’t be able to produce energy properly to fuel these activities. Remember that when energy levels are low, our resources will be directed to the brain first — starving the rest of the body of energy.
The strategy to prevent large dips in glucose is to first prevent large rises. A glycemic excursion in one direction often precipitates an excursion in the opposite direction, and limiting variability is the key to limiting this roller coaster ride of energy. Perhaps the best way to limit large rises (and falls) in glucose is to consume low-glycemic index meals, limit refined carbs, or balance carbohydrate intake with exercise. However, dietary strategies that are successful for controlling blood glucose will vary widely among all of us.
The knowledge of how glucose and glucose variability affect your daily energy levels is important, but so is taking action. By measuring your glucose levels throughout the day — or even at certain time points during the day — you can correlate what’s happening in your body with how you feel. Mapping your energy levels to your blood glucose can allow you to make changes to your diet, exercise routine, or work habits that will allow you to hit peak energy when it matters.
If you experience a mid-day crash, try figuring out whether that’s due to a dip in glucose or whether some other life factor is involved. If you want to time your normal daily peak in glucose and energy with your workout or most cognitively-demanding task of the day, pairing your blood glucose readings with an app like Basis is the first step.
Diet quality, exercise, stress management, and adequate sleep are all variables that impact our blood glucose and the variations in glucose throughout the day. This goes to show that, while glucose is important, we have to consider every aspect of our life when thinking about energy management.
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