Fasting and Women’s Hormones: A Biblical and Science-Based Guide to Fasting Wisely

The Biblical Purpose of Fasting

In Gospel of Matthew 6:16–18, Jesus teaches that fasting is private—not performative. It is not spiritual theater. It is relational.

In Book of Isaiah 58, God rebukes empty fasting—discipline without justice, humility, or obedience.

Biblical fasting is for:

• Drawing nearer to God
• Repentance
• Discernment
• Dependence

Biblical fasting is not:

• A punishment
• A metabolic hack
• A spiritual competition
• A requirement for God’s love

Fasting removes distraction. It does not earn favor.

What Happens in the Body During a Fast?

Now let’s move to physiology.

Fasting is a metabolic stressor. Even when intentional, it triggers adaptive responses.

1. Glycogen Depletion

Within 12–24 hours:

• Liver glycogen declines
• Blood glucose begins to stabilize via gluconeogenesis
• The body shifts toward greater fat oxidation

This is normal metabolic flexibility.

2. Insulin Reduction

Lower insulin levels:

• Increase lipolysis (fat breakdown)
• Improve insulin sensitivity in some individuals

However, improved insulin sensitivity depends heavily on:

• Baseline metabolic health
• Sleep quality
• Stress load
• Total energy balance

3. Autophagy

Extended fasting may stimulate autophagy—a cellular recycling process linked to:

• Removal of damaged proteins
• Cellular repair

But most robust autophagy data comes from animal models. Human evidence is still emerging and context-dependent.

4. Cortisol Activation

Fasting increases cortisol to:

• Maintain blood glucose
• Mobilize stored energy

Short term? Adaptive.Chronic stress + fasting? Potentially disruptive.

Fasting Is a Stress Signal

This is where nuance matters.

The body interprets prolonged energy restriction as:

• Environmental scarcity
• Potential threat

The hypothalamus regulates survival first, reproduction second. That difference is critical when we compare men and women.

Men vs. Women: Biological Differences

Men (Generally)

Short-term fasting in men often shows:

• Improved insulin sensitivity
• Modest fat loss
• Stable testosterone in shorter fasting windows

Men’s reproductive axis is less immediately sensitive to short-term caloric restriction.

But even men can experience:

• Reduced testosterone
• Elevated cortisol
• Decreased training recovery
• Lean mass loss

Especially athletes or highly stressed individuals.

Women: Energy Availability Is Everything

As exercise physiologist Dr. Stacy Sims states:Women are not small men.

• Female physiology is tightly coupled to energy availability.
• The reproductive system is governed by the hypothalamic–pituitary–gonadal (HPG) axis:

Low energy availability →
↓ GnRH →
↓ LH/FSH →
↓ Estrogen & Progesterone

This can result in:

• Irregular cycles
• Anovulation
• Luteal phase defects
• Amenorrhea

Research on Relative Energy Deficiency in Sport (RED-S) shows that insufficient energy intake—whether from intentional restriction or fasting—can impair:

• Bone density
• Thyroid function
• Resting metabolic rate
• Immune function
• Mood stability

Women’s bodies are biologically wired to protect fertility. When energy is scarce, reproduction is downregulated.

Cortisol, Thyroid & Female Stress Response

Fasting activates the HPA axis (hypothalamic–pituitary–adrenal axis).

In some women, especially those who are:

• Highly active
• Under psychological stress
• Sleeping poorly
• In calorie deficit

Fasting can amplify:

• Elevated cortisol
• Suppressed T3 thyroid hormone
• Disrupted sleep
• Increased anxiety

Thyroid conversion (T4 → T3) is sensitive to energy availability. Chronic restriction can reduce metabolic rate.

If fasting causes:

• Sleep disruption
• Mood instability
• Loss of cycle
• Decline in performance

It is not honoring your body.

What the Research Says

• Many fasting studies historically include predominantly male participants.
• Women’s hormonal fluctuations make research design more complex.
• Some time-restricted eating studies show minimal disruption in young, healthy women.
• Other data suggest prolonged restriction may alter reproductive hormones.
• Context matters: age, stress, body composition, training load, and sleep all influence response.

Science is building—but it is not one-size-fits-all.

Fasting Is Not Always the Most Faithful Choice

God is not glorified by burnout, hormone chaos, or under-fueled bodies.

If fasting becomes:

• A tool for body control
• A way to suppress appetite
• A disguised eating disorder
• A competition
• A stress multiplier

It has drifted from its purpose.

Who Should Not Fast from Food

Food-based fasting may not be appropriate for:

• Teenage girls
• Pregnant or breastfeeding women
• Women with a history of disordered eating
• Highly active athletes in season
• Individuals with thyroid dysfunction
• Those experiencing adrenal dysregulation
• Anyone using fasting as punishment

For these individuals, alternative spiritual disciplines are wiser.

Faithful Alternatives

Wisdom may look like:

• Sunrise-to-sunset fasting rather than prolonged restriction
• The Daniel Fast (removing specific foods, not all food)
• Fasting from social media
• Reducing distractions
• Increasing prayer while maintaining adequate fuel

Fueling can also be an act of faith.

The Deeper Question

Before fasting, ask:

Is this coming from humility—or control?
Is this drawing me closer to God—or closer to obsession?
Is my body currently stable—or already stressed?

Sometimes obedience looks like fasting. Sometimes obedience looks like eating. Discernment is maturity.

A prayer for you:

Lord, Help me honor You with my spirit and my body. Give me discernment, not comparison. Teach me when to fast—and when to be fed.
Amen.

Please see the Daniel Fast blog and podcast on the Devotions with Wendi Website for biblical fasting. See my plant based eating plan for tips on meeting food and nutritional needs.