The Endocrinology of Strongman: Hormones That Influence Mass, Strength and Recovery - Episode 9: What Happens Hormally During Caloric Deficit

1. A caloric deficit is an endocrine signal, not just a calorie difference

When energy intake becomes lower than the body's needs, the response is not limited to weight loss. The body changes hormonal signals, autonomic activity, appetite, substrate use, and metabolic priorities. The biological goal is straightforward: preserve essential functions while reducing energy expenditure that is not immediately necessary.

In athletes, especially when a deficit is combined with high training volume, this adaptation can appear as reduced performance, poorer recovery, and changes in endocrine processes that support muscle mass, bone, and reproductive function.

2. Caloric deficit versus low energy availability

A caloric deficit describes, in practical terms, a situation in which the body expends more energy than it receives. Low energy availability, or LEA, considers the energy left for physiological functions after the cost of exercise is subtracted from intake. The concepts overlap, but they are not identical.

This distinction matters for Strongman because a diet that looks reasonable relative to body weight can become inadequate when training demands are very high. LEA literature describes endocrine and metabolic changes in athletes, including changes in leptin, insulin, thyroid hormones, IGF-1, and gonadal hormones.

3. The first major signal: leptin falls

Leptin is produced mainly by adipose tissue and provides the brain with information about energy availability and energy stores. During caloric restriction, especially when fat mass and energy intake fall, leptin tends to decrease.

A fall in leptin does not simply mean that the athlete becomes hungrier. It participates in a broader reorganization of neuroendocrine control: biological pressure to eat rises and the way the body prioritizes energy changes.

4. The hypothalamus receives the message that energy is lower

The hypothalamus integrates signals such as leptin, insulin, ghrelin, and thyroid hormones. During a deficit, this control center changes circuits that influence appetite, energy expenditure, and endocrine function.

From the body's perspective, reduced intake is not merely a nutrition choice. It is a message that resources are more limited. The response is to increase interest in food and reduce some forms of energy expenditure.

5. Insulin tends to fall during energy restriction

When energy intake is reduced, insulin secretion can fall, reflecting lower carbohydrate availability and a different energetic state. This favors fuel mobilization and reduces storage signals.

Lower insulin is not necessarily abnormal. During controlled restriction it can be part of normal physiology. The problem begins when restriction becomes excessive and starts to impair recovery, adaptation, and metabolic function.

6. Glucose can remain normal despite adaptation

The body has several mechanisms for maintaining blood glucose, including changes in insulin secretion, hepatic glucose production, and substrate use. Therefore, normal glucose does not mean that the body has not adapted to energy restriction.

That is why a diet phase should be evaluated in context: body mass, performance, hunger, sleep, recovery, symptoms, and, when indicated, laboratory testing.

7. Cortisol and the response to energy restriction

Severe energy restriction can activate the stress response. A human meta-analysis found increases in cortisol particularly during fasting, whereas less severe forms of caloric restriction did not always produce the same increase.

In sport, cortisol needs to be interpreted together with training load, sleep, and energy availability. An increase may reflect a temporary adaptation, but a persistent context of stress and poor recovery can become problematic.

8. The thyroid adjusts the energy system

One of the best-known responses to energy restriction is a change in thyroid signaling. In some deficit states, T3 can fall, reducing signaling associated with metabolic rate and energy expenditure.

This is often described as metabolic adaptation. It does not mean the thyroid has “shut down,” but that the body is adjusting endocrine activity to conserve energy.

9. Deiodinases and why thyroid adaptation is more complicated

Peripheral conversion of thyroid hormones is influenced by deiodinase enzymes. With low energy availability, changes in peripheral conversion can contribute to a lower active metabolic signal.

Athletes should not turn one T3 value into a diagnosis. A low-T3 pattern can occur during energy restriction and other physiological states and should be distinguished from primary hypothyroidism.

10. GH can stay high while IGF-1 falls

Energy deficit can create an apparently paradoxical state: GH signaling may be preserved or increased while IGF-1 falls. This pattern has been described as relative hepatic GH resistance, in which some of GH's lipolytic effects are preserved while anabolic signaling through IGF-1 is reduced.

For Strongman, the message is important: a “good” GH value on paper does not guarantee an optimally anabolic state. Energy availability matters to how the GH/IGF-1 axis functions.

11. IGF-1 falls when resources are limited

IGF-1 reflects, among other things, the interaction between GH and energy and nutrient availability. In severe restriction, IGF-1 can fall, consistent with a state in which the body reduces prioritization of energetically expensive growth and repair.

Recent experimental literature in athletes also shows that the response is not identical across all studies, especially during short deficits. Magnitude and duration of restriction matter.

12. Testosterone can fall

When energy availability falls, the hypothalamic-pituitary-gonadal axis can be suppressed. In men, some LEA settings are associated with lower LH and testosterone. This is one way the body reduces an energetically costly function when resources are limited.

The evidence does not mean that every caloric deficit automatically causes hypogonadism. Effects depend on severity, duration, body fat, training, sleep, and individual status.

13. Estrogen can change in men too

In men, estradiol is produced largely through aromatization of androgens. If testosterone and adipose tissue change, the estrogenic environment can also change. During severe energy deficiency, these shifts may have implications for bone and reproductive function.

Recent LEA data also show that estradiol changes are less consistent than the fall in leptin and less consistent than some testosterone findings. The system therefore needs to be viewed as a whole rather than as a fixed template for every athlete.

14. Ghrelin raises the pressure to eat

During restriction, hunger signaling can intensify. Ghrelin is one of the main hormones involved in meal initiation and can rise before eating. Energy deficit and weight loss can change the dynamics of these signals.

That is why after several weeks of dieting, hunger can become stronger even when the deficit initially seemed easy to tolerate. Biology begins pushing in the opposite direction.

15. The sympathetic system and energy expenditure

Energy restriction can reduce some components of sympathetic activity and thermogenesis. This contributes to the observation that body-weight loss does not proceed in a perfectly linear fashion.

Less available energy can mean less spontaneous movement, less thermogenesis, and greater energetic efficiency. As a result, the same diet can produce different results early versus late in a weight-loss phase.

16. The body reduces expenditures it considers negotiable

During a deficit, the body prioritizes essential functions and can reduce investment in reproduction, tissue growth, and other metabolically expensive processes. It is a conservation strategy, not a character flaw.

In strength sports, that logic can conflict with the sporting goal. The athlete wants to build and repair tissue, while the body receives a signal that resources are limited.

17. Muscle protein synthesis and energy restriction

During a severe deficit, muscle protein synthesis can be reduced, and energy and amino-acid availability change the context in which muscle fibers respond to training. Adequate protein can limit lean-tissue loss, but it does not completely neutralize an extreme energy deficit.

This leads to an important Strongman rule: preserving muscle during a deficit is a risk-management goal, not a guarantee that hypertrophy will continue at the same rate as during an energy surplus.

18. Strength does not always fall immediately

A Strongman can maintain strength for a period while body mass falls. The nervous system, technique, and experience can compensate for some loss of body mass and glycogen.

But as restriction becomes longer or more aggressive, reduced training volume tolerance, poorer recovery, lower work capacity, and loss of lean mass can appear. Competition performance can suffer before the athlete notices a collapse in a single maximal event.

19. Glycogen and hormones cannot be separated

When carbohydrate and energy intake fall, glycogen availability falls as well. This can influence perceived effort, training volume, and recovery. At the same time, hormonal changes during restriction alter how the body prioritizes fuel use.

For Strongman, an excessively large deficit can therefore produce less glycogen, more hunger, and a more energy-conserving endocrine profile at the same time. It is no surprise that training starts to feel harder.

20. Sleep becomes even more important

Energy restriction and poor sleep can reinforce each other. A deficit can increase hunger and stress, while insufficient sleep can worsen appetite control, insulin sensitivity, and perceived fatigue.

During a fat-loss phase, sleep is not only about muscle recovery. It is part of the endocrine strategy by which the body copes with limited energy.

21. What happens to appetite

As restriction continues, falling leptin and altered hunger signals make dietary adherence harder. This does not mean willpower disappears. The body increases biological pressure for energy intake.

That is why a good diet needs to be moderate enough to sustain. A theoretically perfect plan that creates constant hunger and poor recovery may be inferior to a slower, more sustainable deficit.

22. What happens to resting metabolism

Resting metabolic rate can fall during weight loss for several reasons: a smaller body, less lean mass, thyroid changes, autonomic changes, and altered thermogenesis.

The magnitude is not the same for everyone and does not mean metabolism is “destroyed.” It is better understood as a collection of energy adaptations, some of which improve when intake and body mass normalize.

23. Energy restriction can affect bone

Insufficient energy, together with changes in gonadal hormones, leptin, IGF-1, and thyroid signaling, can alter bone remodeling. Experimental LEA studies have reported increased resorption markers and lower bone-formation markers in some settings.

For Strongman, bone is the foundation supporting heavy loading. A weight-loss strategy that cuts energy too deeply can sacrifice the very tissue the athlete repeatedly stresses.

24. Connective tissues are not protected by being a “big athlete”

Tendons, ligaments, and other collagen-rich tissues need energy and nutrients for remodeling. LEA literature indicates altered collagen turnover under severe energy deficiency.

This means a Strongman can look muscular and powerful externally while the recovery capacity of connective tissues is already under pressure.

25. Immune function can be affected

Severe energy restriction, especially combined with intense training and insufficient sleep, can affect immune function. LEA studies describe changes in immune markers and greater sensitivity to the negative effects of heavy training loads.

For an athlete, repeated minor infections or unexpectedly poor recovery can be a sign that the problem is not only the training program.

26. A caloric deficit is not always bad

A moderate, well-planned deficit can be entirely justified when the goal is reducing body fat, adjusting a weight category, or moving toward competition condition. The body can tolerate periods of restriction without entering a pathological state.

The difference between a useful diet and a problematic one is the magnitude, duration, and context of the deficit, not the simple fact that a calorie gap exists.

27. When the deficit becomes too aggressive

Warning signs can include rapid and persistent performance loss, hard-to-control hunger, deteriorating sleep, reduced libido, irritability, persistent cold sensation, poor recovery, recurrent infections, and excessive loss of lean mass.

None of these findings proves LEA or an endocrine disorder on its own, but a combination deserves attention.

28. Not every study shows the same hormonal change

One of the most important lessons from modern literature is variability. A 2026 systematic review of 13 experimental studies in athletes found that leptin decreased consistently, while T3 and IGF-1 remained stable in most studies and testosterone decreased in about half of the interventions. These differences show that duration, severity, sex, carbohydrate availability, and training context matter.

Endocrinology during a deficit is therefore not an automatic checklist in which every hormone must rise or fall in the same way for every person.

29. Why low carbohydrate availability can amplify the picture

Energy deficit often occurs together with lower carbohydrate intake. This can independently alter insulin, glycogen, T3, and training performance. Some changes attributed to calorie restriction may therefore also be influenced by low carbohydrate availability.

For Strongman, this distinction matters because repeated high-intensity training can have substantial glycogen costs.

30. What happens to hormones during refeeding

When energy intake rises and body mass stabilizes, many of these adaptations can improve. Leptin, insulin, T3, IGF-1, and gonadal hormones can move back toward previous levels, but recovery speed varies.

In literature on physique athletes, testosterone recovery after prolonged restriction has varied considerably between individuals, showing that refeeding is not an instant endocrine switch.

31. What to monitor during a diet

For a Strongman, body weight is only one variable. Event performance, tolerated training volume, sleep, hunger, libido, perceived temperature, mood, and recovery provide practical information about how well the deficit is being tolerated.

When clinically indicated, a physician may evaluate markers such as glucose, HbA1c, TSH, FT4 and, depending on symptoms, gonadal hormones and other parameters. No laboratory profile should be interpreted separately from context.

32. Energy deficit and training adaptation

Training is the stimulus, while energy is the infrastructure that allows the response to that stimulus. When the infrastructure is insufficient, the athlete may still produce force, but the capacity to build, repair, and repeat performance declines.

That is why the same program can produce different results in an energy surplus versus an aggressive deficit. It is not only the diet that changed. The endocrine environment in which adaptation occurs changed as well.

33. What all of this means for Strongman

A Strongman typically carries substantial muscle mass, has high energy expenditure, and can have training demands that are difficult to combine with a large deficit. When fat loss is the goal, the deficit should be designed to preserve as much lean mass and work capacity as possible.

Close to competition, the problem becomes even more delicate: rapid mass loss can alter water, glycogen, appetite, hormones, and work capacity. A lighter scale weight is not automatically a better-performing athlete.

34. The myth that you need to “keep hormones low” to lose fat

Lower insulin, leptin, or T3 can occur during a deficit, but these changes are not performance goals. They are physiological responses to low energy availability. Lower is not automatically better.

The success of a diet should not be measured by how “low” hormones become, but by the result achieved with an acceptable physiological cost.

35. Conclusion

A caloric deficit is a state in which the body changes endocrine priorities. Leptin and insulin tend to fall, thyroid signaling can change, IGF-1 can fall, and the stress response can rise, particularly when the deficit is severe. The reproductive axis can also be affected, while appetite becomes biologically harder to control.

For Strongman, the lesson is not to avoid every deficit, but to understand the physiological price of an overly aggressive one. Fat loss can be a tool. When energy becomes too low for the demands of the body and training, endocrinology starts changing the rules of the game.

Selected references

1. Jeppesen JS, Hellsten Y, Melin AK, Hansen M. Short-Term Severe Low Energy Availability in Athletes: Molecular Mechanisms, Endocrine Responses, and Performance Outcomes—A Narrative Review. Scandinavian Journal of Medicine & Science in Sports. 2025;35(6):e70089. DOI: 10.1111/sms.70089.

2. Biochemical Responses to Experimentally Induced Short-Term Low Energy Availability in Athletes: A Systematic Review. Scandinavian Journal of Medicine & Science in Sports. 2026. DOI: 10.1111/sms.70249.

3. Mountjoy M et al. IOC consensus statement on Relative Energy Deficiency in Sport (RED-S): 2018 update. British Journal of Sports Medicine. 2018.

4. Contemporary literature on exercise, endocrine adaptation, and low energy availability in athletes.

5. Caloric restriction: impact upon pituitary function and reproduction. Review literature on GnRH, LH, leptin, insulin and IGF-1 during energy restriction.

6. Relative energy deficiency in sports (RED-S): elucidation of endocrine changes affecting the health of males and females. Review of reproductive, thyroid, metabolic and appetite-regulating adaptations.

7. Systematic review and meta-analysis of cortisol responses to fasting and caloric restriction in humans.

8. After the spotlight: evidence-based considerations for recovery from prolonged energy restriction in physique athletes.

9. Effects of low energy availability on performance in male athletes: a scoping review. Journal of Science and Medicine in Sport. 2025.

10. Rethinking Energy Availability from Conceptual Models to Applied Practice: A Narrative Review. Contemporary review of endocrine and metabolic adaptation to low energy availability.