January 2025

Cycles

• Cycles Of Life
• The Sun Cycle – Circadian Rhythm
• Metabolic Cycles
• The Moon Cycle – Reproductive Rhythm

Last week, I wrote about the sun’s effect on the hormonal system. I focused on how the sun affects cortisol and how aligning one’s inner clocks with the cosmic clock benefits sleep, stress, and alertness. Today, I focus on the connection of the circadian cycle to metabolism.

Metabolic Cycles

It all starts in the hypothalamus, the control panel of the endocrine system that sends hormone messengers to the pituitary gland. These hormones start a cascade of hormonal messengers, eventually soaking every body cell in a hormonal soap.

Many diets address what you eat to lose weight, reduce blood glucose, increase insulin sensitivity, and increase energy production. But as I found out, not just what you eat but also when you eat has a huge impact on how your body utilizes food.

Four types of metabolic hormones are affected by the circadian cycle:

• Growth hormones
• The thyroid hormone
• Ghrelin, the hunger hormone
• Glucose and Insulin

Circadian cycle and growth hormones

Growth hormones are vital for tissue and muscle growth and repair, setting metabolic rate and energy levels. They are especially important in developing children, who are still growing and developing their bodies.

Growth hormones are secreted during NREM deep sleep, the part of the circadian cycle when cortisol is low and melatonin is high.

When my brother was a teenager, he returned from school, ate, and slept. My mom used to joke that you can hear him grow if you stand quietly by his door. There is a grain of truth to that joke. 😀

Deep sleep is crucial for many reasons, one is that it repairs the daily wear and tear your body endures. Healing improves when your body is supported by the circadian cycle.

The circadian cycle and the thyroid

Thyroid hormones are the hormones that regulate metabolism in the body.

The master pacekeeper, the hypothalamus, releases TRH, which prompts the pituitary gland to produce TSH (Thyroid-Stimulating Hormone), which initiates thyroid hormone production in the thyroid gland.

 The thyroid gland produces thyroid hormones that initiate energy production in the cells.

Excess thyroid hormones, hyperthyroidism lead to heightened metabolism, weight loss, heat sensitivity, and restlessness. Deficient thyroid, hypothyroid, is a lower metabolic rate that feels like fatigue, cold sensitivity, and weight gain.

 Research suggests that circulating TSH levels exhibit a clear daily rhythm. Plasma concentrations rise in the early evening before sleep and reach maximal levels between 2 and 4 in the early morning. TSH concentration then declines during the rest of the sleep until low daytime levels are reached. TSH is at its lowest level between two and four in the afternoon.

T4 strongly echoes the nightly TSH rise in a person with a healthy thyroid and pituitary gland. The FT4 has a delayed wave and a flatter rise and fall.

The circadian cycle and thyroid conditions can create a vicious cycle.

 If your circadian cycle is disrupted by stress, night shifts, or because you are a night owl, your thyroid hormone production might be dysregulated, leading to either excess or deficiency in TSH.

On the other hand, dysregulated thyroid hormones can mess with your sleep. People with hypothyroidism conditions often feel cold at night and struggle with joint and muscle pain. People with hyperthyroidism feel restless and too warm many times. In both cases, sleep is disrupted, as is the circadian cycle.

Circadian cycle glucose and insulin

Let’s first understand the role of glucose and insulin in the body.

 Glucose is the fuel that fuels metabolism. Cells get glucose from the blood for energy production so they can function. Blood glucose increases either after a meal or following a cortisol surge because cortisol prompts muscles and the liver to release glucose into the blood.

Once glucose is in the blood, it needs help entering the cells. Most cells in the body (muscle cells are the exception to this rule) need a “key” to open their doors to glucose. That key is insulin.

 The blue morning light causes a surge of cortisol, immediately promoting glucose release from the liver to the blood in anticipation of the body’s increasing energy needs.

The pancreas immediately reacts to increased blood glucose with a surge of insulin. Insulin secretion follows a circadian rhythm, with a high in the morning and a slow decline toward the evening, when cortisol and glucose are reduced, too.

A heavy meal in the evening, stress, and insomnia that spikes cortisol and glucose in the evening can lead to high glucose levels with lower insulin levels that are pro-inflammatory.

In many countries, people eat the main meal of the day at noon and enjoy a light meal in the evening to align their digestion and absorption with the circadian cycle and the cycle of glucose metabolism and insulin secretion.

The circadian cycle hunger and satiation

Gherlin, the hormone that causes hunger, follows a circadian rhythm. It is highest in the morning before breakfast and decreases following meals but rises again between meals.

Ghrelin production will follow your habits. If you eat at the same time every day, your body will anticipate the meal and secrete ghrelin right beforehand.

For metabolic health, eating breakfast like a queen, lunch like a princess, and supper like a popper is recommended.

When cortisol levels peak in the morning, you are up and ready to be active, so you need the fuel food provides. In the morning, insulin sensitivity is also higher, setting the tone for glucose metabolism throughout the day.

In the evenings, ghrelin is at its lowest because the body’s energy needs are also at their lowest. Therefore, you will benefit from a light supper.  

Metabolic conditions are the most common chronic health conditions people in the Western world struggle with. These conditions are complicated because the circadian cycle affects every system in the body.

Creating a care plan to address metabolic conditions should include what you eat and your meal times, stress, and sleep.

The circadian cycle and the microbiome

I love learning about the microbiome because it is another example of how the lines between our bodies and nature are blurred. But did you know your microbiome follows the sun’s trail in the sky from sunrise to sunset?

The research found evidence that the circadian cycle and gut microbiome have a bidirectional effect.

The circadian promotes rhythmical changes in mucus production in the gut, prompting bacterial populations to fluctuate throughout 24-hour cycles. Gut microbiome has its own circadian cycle, with different species becoming more active at different times.

On the other hand,  gut bacteria modulate host rhythms via microbial metabolites such as butyrate, polyphenolic derivatives, vitamins, and amines that regulate the sleep-wake cycle by neurotransmitters (like GABA and serotonin) and mediating inflammation.

 When circadian rhythms are disturbed:

• Bacterial populations become imbalanced
• Increased intestinal permeability occurs
• Inflammatory responses increase
• Metabolic processes become less efficient.
• The risk of dysbiosis increases

Supporting circadian rhythm by creating a daily routine of meals and sleep is essential for a healthy microbiome.

The liver and circadian cycle

The liver is involved in glucose and fat metabolism and the detoxification process. Liver function, too, is affected by the circadian cycle.

In the morning, the liver is more active; therefore, it demonstrates:

• Higher glucose processing capacity
• Enhanced insulin sensitivity
• Increased nutrient absorption
• Peak detoxification activity
• Higher metabolic rate

In the evening, the liver’s capacity to process glucose and detox is reduced because of:

• Lower enzyme production
• Increased oxidative stress
• Reduced blood flow to the liver

 The liver focuses on repair and regeneration during the evenings. The fluctuation in liver function throughout the day supports the belief that eating the main meal earlier in the day when the liver capacities peak.

 Metabolic conditions are the most common chronic health conditions people in the Western world struggle with. These conditions are complicated because the circadian cycle affects every system in the body.

 Creating a care plan to address metabolic conditions should include what you eat and your meal times, stress, and sleep.

 Other aspects of metabolic conditions include the connection between the liver and the circadian cycle and the metabolism of fat, protein, and carbohydrates throughout the day. There is so much more to explore, and I am intrigued. What about you?