Low-Fat Diets

 

Low-Fat Diets: Benefits, Limitations, and the Science Behind Fat Restriction

Revisiting one of the most influential dietary paradigms in modern nutrition

Introduction

For decades, low-fat diets dominated nutritional advice worldwide. Beginning in the late 20th century, public health authorities promoted fat restriction as a primary strategy to combat obesity and cardiovascular disease. This approach shaped food industries, dietary guidelines, and public perception—often equating “low-fat” with “healthy.”

Yet, contemporary research has complicated this narrative. While fat reduction offers certain benefits, overly restrictive or poorly planned low-fat diets may lead to unintended consequences.

This article provides a comprehensive, evidence-based examination of low-fat diets—their physiology, benefits, risks, and practical application in modern healthcare.

What is a Low-Fat Diet?

A low-fat diet typically limits fat intake to less than 30% of total daily calories, with stricter versions reducing it to 20% or lower.

Types of Low-Fat Diets

• Moderate low-fat: 25–30% of total calories from fat
• Very low-fat: <20% of total calories
• Ultra low-fat (therapeutic): <10% (used in specific clinical programs)

Popular examples include structured programs like the Ornish Diet and the Pritikin Diet.

Physiological Basis

Dietary fats are energy-dense macronutrients that:

• Provide essential fatty acids
• Aid in absorption of fat-soluble vitamins (A, D, E, K)
• Support hormone synthesis

Reducing fat intake leads to:

1. Lower caloric density of meals
2. Reduced intake of saturated fats
3. Potential shifts toward carbohydrate-based energy metabolism

Unlike carbohydrate restriction, low-fat diets do not typically induce Ketosis.

Potential Benefits of Low-Fat Diets

1. Cardiovascular Health

One of the primary reasons for adopting low-fat diets is to reduce cardiovascular risk.

Evidence suggests that reducing saturated fat intake can:

• Lower LDL cholesterol
• Improve arterial function

This is particularly relevant in preventing coronary artery disease.

2. Weight Management

Because fat contains 9 kcal/g (compared to 4 kcal/g for carbohydrates and protein), reducing fat intake can:

• Lower overall caloric intake
• Promote gradual weight loss

However, effectiveness depends heavily on overall diet quality.

3. Improved Lipid Profile

Low-fat diets often lead to:

• Reduction in total cholesterol
• Decrease in LDL cholesterol

Though they may also reduce HDL (“good cholesterol”) in some cases.

4. Reduced Risk of Certain Chronic Diseases

Some studies suggest benefits in:

• Hypertension
• Certain cancers (especially when combined with high fiber intake)

Dietary patterns emphasizing plant-based, low-fat foods appear particularly protective.

5. Compatibility with Public Health Guidelines

Organizations like the World Health Organization have historically supported moderate fat restriction, especially reducing saturated and trans fats.

Potential Risks and Drawbacks

1. Nutrient Deficiencies

Very low-fat diets may impair absorption of:

• Fat-soluble vitamins (A, D, E, K)
• Essential fatty acids (omega-3 and omega-6)

This can lead to deficiencies if not carefully planned.

2. Increased Carbohydrate Intake

A major criticism is that reducing fat often leads to increased consumption of refined carbohydrates:

• Sugars
• Processed grains

This may worsen:

• Type 2 Diabetes
• Metabolic Syndrome

3. Reduced Satiety

Fat contributes to:

• Flavor
• Fullness

Low-fat diets may lead to:

• Increased hunger
• Higher frequency of eating

This can paradoxically hinder weight loss.

4. Hormonal Effects

Dietary fats are essential for hormone production. Extremely low fat intake may affect:

• Sex hormones
• Steroid hormones

This is particularly relevant in long-term restrictive diets.

5. Decline in HDL Cholesterol

While LDL often decreases, HDL levels may also drop, which could negatively impact cardiovascular risk balance.

6. Sustainability Issues

Strict low-fat diets may be:

• Less palatable
• Difficult to maintain long-term

Adherence is a key determinant of success in any dietary pattern.

Low-Fat vs Low-Carb: The Ongoing Debate

Modern research indicates that both low-fat and low-carb diets can be effective for weight loss and metabolic health when:

• Calorie intake is controlled
• Food quality is high

Large trials show that differences between these diets often diminish over time, emphasizing adherence over macronutrient composition.

Healthy vs Unhealthy Low-Fat Diets

Healthy Low-Fat Approach

• Whole grains
• Fruits and vegetables
• Legumes
• Lean proteins

Unhealthy Low-Fat Approach

• Processed “low-fat” foods high in sugar
• Refined carbohydrates
• Artificial additives

The “low-fat” label does not automatically imply healthfulness.

Practical Guidelines

For those considering a low-fat diet:

1. Prioritize whole foods over processed options
2. Include sources of healthy fats (in moderation)
3. Avoid excess refined carbohydrates
4. Ensure adequate intake of fat-soluble vitamins
5. Monitor lipid profile and metabolic markers
6. Adopt a balanced, sustainable eating pattern

Conclusion

Low-fat diets have played a pivotal role in shaping modern nutritional science and public health policy. They offer clear benefits in reducing cardiovascular risk factors and can support weight management when properly implemented.

However, they are not without limitations. Poorly planned low-fat diets—especially those high in refined carbohydrates—may undermine metabolic health.

The current scientific consensus increasingly favors diet quality over strict macronutrient restriction. A balanced approach that includes healthy fats, whole foods, and individualized planning is likely to yield the best long-term outcomes.

 

Luteinizing hormone/ interstitial cell stimulating hormone (ICSH)

 

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Luteinizing hormone/ interstitial cell stimulating hormone (ICSH)

Introduction

Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. In females, an acute rise of LH known as an LH surge, triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistically with follicle-stimulating hormone (FSH). The term luteinizing comes from the Latin "luteus", meaning "yellow". This is in reference to the corpus luteum, which is a mass of cells that forms in an ovary after an ovum (egg) has been discharged. The corpus luteum is so named because it often has a distinctive yellow color. The process of forming the corpus luteum is known as "luteinization", and thus the hormone that triggers this process is termed the "luteinizing" hormone.

Structure

LH is a heterodimeric glycoprotein. Each monomeric unit is a glycoprotein molecule; one alpha and one beta subunit make the full, functional protein. Its structure is similar to that of the other glycoprotein hormones, follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG).

The protein dimer contains 2 glycopeptidic subunits (labeled alpha- and beta- subunits) that are non-covalently associated:

The alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino acids in human. The beta subunits vary. LH has a beta subunit of 120 amino acids (LHB) that confers its specific biologic action and is responsible for the specificity of the interaction with the LH receptor.

Functions

In both males and females, LH/ICSH works upon endocrine cells in the gonads to produce androgens.

Effects in females

LH supports theca cells in the ovaries that provide androgens and hormonal precursors for estradiol production. At the time of menstruation, FSH initiates follicular growth, specifically affecting granulosa cells. With the rise in estrogens, LH receptors are also expressed on the maturing follicle, which causes it to produce more estradiol. Eventually, when the follicle has fully matured, a spike in 17α-hydroxyprogesterone production by the follicle inhibits the production of estrogens. Previously, the preovulatory LH surge was attributed to a decrease in estrogen-mediated negative feedback of GnRH in the hypothalamus, subsequently stimulating the release of LH from the anterior pituitary. Some studies, however, attribute the LH surge to positive feedback from estradiol after production by the dominant follicle exceeds a certain threshold. 

Exceptionally high levels of estradiol induce hypothalamic production of progesterone, which stimulates elevated GnRH secretion, triggering a surge in LH. The increase in LH production only lasts for 24 to 48 hours. This "LH surge" triggers ovulation, thereby not only releasing the ovum from the follicle, but also initiating the conversion of the residual follicle into a corpus luteum that, in turn, produces progesterone to prepare the endometrium for a possible implantation. LH is necessary to maintain luteal function for the second two weeks of the menstrual cycle. If pregnancy occurs, LH levels will decrease, and luteal function will instead be maintained by the action of hCG (human chorionic gonadotropin), a hormone very similar to LH but secreted from the new placenta.

Effects in males

ICSH acts upon the Leydig cells of the testis and is regulated by gonadotropin-releasing hormone (GnRH). The Leydig cells produce testosterone under the control of ICSH. ICSH binds to LH receptors on the membrane surface of Leydig cells. Binding to this receptor causes an increase in cyclic adenosine monophosphate (cAMP), a secondary messenger, which allows cholesterol to translocate into the mitochondria. Within the mitochondria, cholesterol is converted to pregnenolone by CYP11A1. Pregnenolone is then converted to dehydroepiandrosterone (DHEA). DHEA is then converted to androstenedione by 3β-hydroxysteroid dehydrogenase (3β-HSD) and then finally converted to testosterone by 17β-hydroxysteroid dehydrogenase (HSD17B). The onset of puberty is controlled by two major hormones: FSH initiates spermatogenesis and ICSH signals the release of testosterone, an androgen that exerts both endocrine activity and intratesticular activity on spermatogenesis.

LH is released from the pituitary gland, and is controlled by pulses of gonadotropin-releasing hormone. When bloodstream testosterone levels are low, the pituitary gland is stimulated to release LH. As the levels of testosterone increase, it will act on the pituitary through a negative feedback loop and inhibit the release of GnRH and LH consequently. Androgens (including testosterone and dihydrotestosterone) inhibit monoamine oxidase (MAO) in the pineal gland, leading to increased melatonin and reduced LH and FSH by melatonin-induced increase of gonadotropin-inhibitory hormone (GnIH) synthesis and secretion. Testosterone can also be aromatized into estradiol (E2) to inhibit LH. E2 decreases pulse amplitude and responsiveness to GnRH from the hypothalamus onto the pituitary.

Changes in LH and testosterone blood levels and pulse secretions are induced by changes in sexual arousal in human males.

Effects in the brain

Luteinizing hormone receptors are located in areas of the brain associated with cognitive function. The role of LH role in the central nervous system (CNS) may be of relevance to understanding and treating post-menopausal cognitive decline.

Normal levels

During reproductive years, typical levels are between 1 and 20 IU/L. Physiologic high LH levels are seen during the LH surge (v.s.) and typically last 48 hours. In males over 18 years of age, reference ranges have been estimated to be 1.8–8.6 IU/L.

LH is measured in international units (IU). When quantifying the amount of LH in a sample in IUs, it is important to know which international standard your lot of LH was calibrated against since they can vary broadly from year to year. For human urinary LH, one IU is defined as 1/189th of an ampule denoted 96/602 and distributed by the NIBSC, corresponding to approximately 0.04656 μg of LH protein for a single IU, but older standard versions are still widely in use.

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Antidiuretic Hormone/ vasopressin

 

Antidiuretic Hormone / vasopressin

Introduction

Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travels down the axon terminating in the posterior pituitary, and is released from vesicles into the circulation in response to extracellular fluid hypertonicity (hyperosmolality).

Structure

The vasopressins are peptides consisting of nine amino acids (nonapeptides). The amino acid sequence of arginine vasopressin (argipressin) is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, with the cysteine residues forming a disulfide bond and the C-terminus of the sequence converted to a primary amide. Lysine vasopressin (lypressin) has a lysine in place of the arginine as the eighth amino acid, and is found in pigs and some related animals, whereas arginine vasopressin is found in humans. The structure of oxytocin is very similar to that of the vasopressins.

Production and secretion

The physiological stimulus for secretion of vasopressin is increased osmolality of the plasma, monitored by the hypothalamus. A decreased arterial blood volume, (such as can occur in cirrhosis, nephrosis, and heart failure), stimulates secretion, even in the face of decreased osmolality of the plasma: it supersedes osmolality, but with a milder effect. The AVP that is measured in peripheral blood is almost all derived from secretion from the posterior pituitary gland (except in cases of AVP-secreting tumours). Vasopressin is produced by magnocellular neurosecretory neurons in the paraventricular nucleus of hypothalamus (PVN) and supraoptic nucleus (SON). It then travels down the axon through the infundibulum within neurosecretory granules that are found within Herring bodies, localized swellings of the axons and nerve terminals. These carry the peptide directly to the posterior pituitary gland, where it is stored until released into the blood. It has a very short half-life, between 16 and 24 minutes.

Regulation

Vasopressin is regulated by AVP gene expression which is managed by major clock controlled genes. In this circadian circuit known as the transcription-translation feedback loop (TTFL). Many factors influence the secretion of vasopressin:

 

·       Ethanol (alcohol) reduces the calcium-dependent secretion of AVP by blocking voltage-gated calcium channels in neurohypophyseal nerve terminals in rats.

·       Angiotensin II stimulates AVP secretion, in keeping with its general pressor and pro-volumic effects on the body.

·       Atrial natriuretic peptide(ANP) inhibits AVP secretion, in part by inhibiting Angiotensin II-induced stimulation of AVP secretion.

·       Cortisol inhibits secretion of antidiuretic hormone.

Functions

Vasopressin regulates the tonicity of body fluids. It is released from the posterior pituitary in response to hypertonicity and causes the kidneys to reabsorb solute-free water and return it to the circulation from the tubules of the nephron, thus returning the tonicity of the body fluids toward normal. An incidental consequence of this renal reabsorption of water is concentrated urine and reduced urine volume. AVP released in high concentrations may also raise blood pressure by inducing moderate vasoconstriction. Details as given below-

A.      Kidneys

ADH or Vasopressin has three main effects which are:

1.       Increasing the water permeability of cortical collecting tubules (CCT), as well as outer and inner medullary collecting duct (OMCD & IMCD) in the kidney, thus allowing water reabsorption and excretion of more concentrated urine, i.e., antidiuresis. This occurs through increased transcription and insertion of water channels (Aquaporin-2) into the apical membrane of collecting tubule and collecting duct epithelial cells.[16][17] Aquaporins allow water to move down their osmotic gradient and out of the nephron, increasing the amount of water re-absorbed from the filtrate (forming urine) back into the bloodstream. This effect is mediated by V2 receptors. Vasopressin also increases the concentration of calcium in the collecting duct cells, by episodic release from intracellular stores. Vasopressin, acting through cAMP, also increases transcription of the aquaporin-2 gene, thus increasing the total number of aquaporin-2 molecules in collecting duct cells.

2.       Increasing permeability of the inner medullary portion of the collecting duct to urea by regulating the cell surface expression of urea transporters,[19] which facilitates its reabsorption into the medullary interstitium as it travels down the concentration gradient created by removing water from the connecting tubule, cortical collecting duct, and outer medullary collecting duct.

3.       Acute increase of sodium absorption across the ascending loop of Henle. This adds to the countercurrent multiplication which aids in proper water reabsorption later in the distal tubule and collecting duct.

B. Central nervous system

Vasopressin released within the brain may have several actions:

1.       Vasopressin is released into the brain in a circadian rhythm by neurons of the suprachiasmatic nucleus.

2.       Vasopressin released from posterior pituitary is associated with nausea.

3.       Recent evidence suggests that vasopressin may have analgesic effects. The analgesia effects of vasopressin were found to be dependent on both stress and gender.

Medical uses

1.       Vasopressin is used to manage anti-diuretic hormone deficiency. Vasopressin is used to treat diabetes insipidus related to low levels of antidiuretic hormone. It is available as Pressyn.

2.       Vasopressin has off-label uses and is used in the treatment of vasodilatory shock, gastrointestinal bleeding, ventricular tachycardia and ventricular fibrillation.

3.       Vasopressin agonists are used therapeutically in various conditions, and its long-acting synthetic analogue desmopressin is used in conditions featuring low vasopressin secretion, as well as for control of bleeding.

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Growth hormone

 

Growth hormone

Introduction

Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in human development. GH also stimulates production of insulin-like growth factor 1 (IGF-1) and increases the concentration of glucose and free fatty acid. It is a type of mitogen which is specific only to the receptors on certain types of cells. GH is a 191-amino acid, single-chain polypeptide that is synthesized, stored and secreted by somatotropic cells within the lateral wings of the anterior pituitary gland. A recombinant form of HGH called somatropin (INN) is used as a prescription drug to treat children's growth disorders and adult growth hormone deficiency.

Genes for human growth hormone, known as growth hormone 1 (somatotropin; pituitary growth hormone) and growth hormone 2 (placental growth hormone; growth hormone variant), are localized in the q22-24 region of chromosome and are closely related to human chorionic somatomammotropin (also known as placental lactogen) genes. GH, human chorionic somatomammotropin, and prolactin belong to a group of homologous hormones with growth-promoting and lactogenic activity.

Structure

The major isoform of the human growth hormone is a protein of 191 amino acids and a molecular weight of 22,124 daltons. The structure includes four helices necessary for functional interaction with the GH receptor. Several molecular isoforms of GH exist in the pituitary gland and are released to blood. In particular, a variant of approximately 20 kDa originated by an alternative splicing is present in a rather constant 1:9 ratio.

Regulation

Secretion of growth hormone (GH) in the pituitary is regulated by the neurosecretory nuclei of the hypothalamus. These cells release the peptides growth hormone-releasing hormone (GHRH or somatocrinin) and growth hormone-inhibiting hormone (GHIH or somatostatin) into the hypophyseal portal venous blood surrounding the pituitary. GH release in the pituitary is primarily determined by the balance of these two peptides, which in turn is affected by many physiological stimulators (e.g., exercise, nutrition, sleep) and inhibitors (e.g., free fatty acids) of GH secretion.

Somatotropic cells in the anterior pituitary gland then synthesize and secrete GH in a pulsatile manner, in response to these stimuli by the hypothalamus. The largest and most predictable of these GH peaks occurs about an hour after onset of sleep with plasma levels of 13 to 72 ng/mL Maximal secretion of GH may occur within minutes of the onset of slow-wave (SW) sleep (stage III or IV). Otherwise there is wide variation between days and individuals. Nearly fifty percent of GH secretion occurs during the third and fourth NREM sleep stages. Surges of secretion during the day occur at 3- to 5-hour intervals. The plasma concentration of GH during these peaks may range from 5 to even 45 ng/mL. Between the peaks, basal GH levels are low, usually less than 5 ng/mL for most of the day and night.

A number of factors are known to affect GH secretion, such as age, sex, diet, exercise, stress, and other hormones. Young adolescents secrete GH at the rate of about 700 μg/day, while healthy adults secrete GH at the rate of about 400 μg/day.[20] Sleep deprivation generally suppresses GH release, particularly after early adulthood.[21]

Stimulators[quantify] of growth hormone (GH) secretion include:

·       Peptide hormones

·       GHRH (somatocrinin) through binding to the growth hormone-releasing hormone receptor (GHRHR)

·       Ghrelin through binding to growth hormone secretagogue receptors (GHSR)

·       Sex hormones

o   Increased androgen secretion during puberty (in males from testes and in females from adrenal cortex)

o   Testosterone and DHEA

o   Estrogen

·       Clonidine, moxonidine and L-DOPA by stimulating GHRH release, α4β2 nicotinic agonists, including nicotine, which also act synergistically with clonidine or moxonidine.[

·       Hypoglycemia,

·       arginine, pramipexole, ornitine, lysine, tryptophan, γ-Aminobutyric acid and propranolol by inhibiting somatostatin release

·       Deep sleep

·       Glucagon

·       Sodium oxybate or γ-Hydroxybutyric acid

·       Niacin as nicotinic acid (vitamin B3)

·       Fasting

·       Insulin

·       Vigorous exercise

Inhibitors[quantify] of GH secretion include:

·       GHIH (somatostatin) from the periventricular nucleus

·       circulating concentrations of GH and IGF-1 (negative feedback on the pituitary and hypothalamus)

·       Hyperglycemia

·       Glucocorticoids

·       Dihydrotestosterone

·       Phenothiazines

Functions

Effects of growth hormone on the tissues of the body can generally be described as anabolic (building up). Like most other peptide hormones, GH acts by interacting with a specific receptor on the surface of cells. Increased height during childhood is the most widely known effect of GH. Height appears to be stimulated by at least two mechanisms-

1.       Because polypeptide hormones are not fat-soluble, they cannot penetrate cell membranes. Thus, GH exerts some of its effects by binding to receptors on target cells, where it activates the MAPK/ERK pathway. Through this mechanism GH directly stimulates division and multiplication of chondrocytes of cartilage.

2.       GH also stimulates, through the JAK-STAT signaling pathway, the production of insulin-like growth factor 1 (IGF-1, formerly known as somatomedin C), a hormone homologous to proinsulin.[40] The liver is a major target organ of GH for this process and is the principal site of IGF-1 production. IGF-1 has growth-stimulating effects on a wide variety of tissues. Additional IGF-1 is generated within target tissues, making it what appears to be both an endocrine and an autocrine/paracrine hormone. IGF-1 also has stimulatory effects on osteoblast and chondrocyte activity to promote bone growth.

In addition to increasing height in children and adolescents, growth hormone has many other effects on the body:

·       Increases calcium retention, and strengthens and increases the mineralization of bone

·       Increases muscle mass through sarcomere hypertrophy

·       Promotes lipolysis

·       Increases protein synthesis

·       Stimulates the growth of all internal organs excluding the brain

·       Plays a role in homeostasis

·       Reduces liver uptake of glucose

·       Promotes gluconeogenesis in the liver

·       Contributes to the maintenance and function of pancreatic islets

·       Stimulates the immune system

·       Increases deiodination of T4 to T3

·       Induces insulin resistance

Leptin

 

Leptin

Introduction

Leptin (from Greek λεπτός leptos, "thin" or "light" or "small"), also known as obese protein, is a protein hormone predominantly made by adipocytes (cells of adipose tissue). Its primary role is likely to regulate long-term energy balance.

As one of the major signals of energy status, leptin levels influence appetite, satiety, and motivated behaviors oriented toward the maintenance of energy reserves (e.g., feeding, foraging behaviors).

The amount of circulating leptin correlates with the amount of energy reserves, mainly triglycerides stored in adipose tissue. High leptin levels are interpreted by the brain that energy reserves are high, whereas low leptin levels indicate that energy reserves are low, in the process adapting the organism to starvation through a variety of metabolic, endocrine, neurobiochemical, and behavioral changes. Leptin is coded for by the LEP gene. Leptin receptors are expressed by a variety of brain and peripheral cell types. These include cell receptors in the arcuate and ventromedial nuclei, as well as other parts of the hypothalamus and dopaminergic neurons of the ventral tegmental area, consequently mediating feeding.

Although regulation of fat stores is deemed to be the primary function of leptin, it also plays a role in other physiological processes, as evidenced by its many sites of synthesis other than fat cells, and the many cell types beyond hypothalamic cells that have leptin receptors. Many of these additional functions are yet to be fully defined.

In obesity, a decreased sensitivity to leptin occurs (similar to insulin resistance in type 2 diabetes), resulting in an inability to detect satiety despite high energy stores and high levels of leptin.

Sites of synthesis

Leptin is produced primarily in the adipocytes of white adipose tissue. It also is produced by brown adipose tissue, placenta (syncytiotrophoblasts), ovaries, skeletal muscle, stomach (the lower part of the fundic glands), mammary epithelial cells, bone marrow,[19] gastric chief cells, and P/D1 cells.

Blood levels

Leptin circulates in blood in free form and bound to proteins. Leptin levels vary exponentially, not linearly, with fat mass. Leptin levels in blood are higher between midnight and early morning, perhaps suppressing appetite during the night. The diurnal rhythm of blood leptin levels may be modified by meal-timing. Increased levels of melatonin causes a downregulation of leptin, however, melatonin also appears to increase leptin levels in the presence of insulin, therefore causing a decrease in appetite during sleeping. Partial sleep deprivation has also been associated with decreased blood leptin levels.

Functions

1.       Predominantly, the "energy expenditure hormone" leptin is made by adipose cells, and is thus labeled fat cell-specific. The central location of action (effect) of the fat cell-specific hormone leptin is the hypothalamus. The primary function of the hormone leptin is the regulation of adipose tissue mass through central hypothalamus mediated effects on hunger, food energy use, physical exercise, and energy balance.

2.       Outside the brain, in the periphery of the body, leptin's secondary functions are: modulation of energy expenditure, modulation between fetal and maternal metabolism, and that of a permissive factor in puberty, activator of immune cells, activator of beta islet cells, and growth factor.

3.       Leptin along with kisspeptin controls the onset of puberty. High levels of leptin, as usually observed in obese females, can trigger neuroendocrine cascade resulting in early menarche. This may eventually lead to shorter stature as estrogen secretion starts during menarche and causes early closure of epiphyses.

4.       Leptin can affect bone metabolism via direct signalling from the brain. Leptin decreases cancellous bone, but increases cortical bone. This "cortical-cancellous dichotomy" may represent a mechanism for enlarging bone size, and thus bone resistance, to cope with increased body weight.

5.       Factors that acutely affect leptin levels are also factors that influence other markers of inflammation, e.g., testosterone, sleep, emotional stress, caloric restriction, and body fat levels. While it is well-established that leptin is involved in the regulation of the inflammatory response, it has been further theorized that leptin's role as an inflammatory marker is to respond specifically to adipose-derived inflammatory cytokines.

6.       Similar to what is observed in chronic inflammation, chronically elevated leptin levels are associated with obesity, overeating, and inflammation-related diseases, including hypertension, metabolic syndrome, and cardiovascular disease. While leptin is associated with body fat mass, the size of individual fat cells, and overeating, it is not affected by exercise.

specific conditions

In humans, many instances are seen where leptin dissociates from the strict role of communicating nutritional status between body and brain and no longer correlates with body fat levels:

·       Leptin plays a critical role in the adaptive response to starvation.

·       Leptin level is decreased after short-term fasting (24–72 hours), even when changes in fat mass are not observed.

·       Serum level of leptin is reduced by sleep deprivation.

·       Leptin levels are paradoxically increased in obesity.

·       Leptin level is increased by emotional stress.

·       Leptin level is chronically reduced by physical exercise training.

·       Leptin level is decreased by increases in testosterone levels and increased by increases in estrogen levels.

·       Leptin level is increased by insulin.

·       Leptin release is increased by dexamethasone.

·       In obese patients with obstructive sleep apnea, leptin level is increased, but decreased after the administration of continuous positive airway pressure.[119][120] In non-obese individuals, h