Protein is associated with the building of muscle, tissue repair and the maintenance of bodily strength. But its role extends beyond these functions. “Almost every function in our body depends on protein in some way. It helps the body produce certain hormones, transport them through the bloodstream, and regulate processes involved in metabolism, appetite and reproduction,” says Dr. Janani Subburaj, an integrative lifestyle practitioner and founder of YogAhara Wellness.
Proteins are made up of smaller units called amino acids. All nine essential amino acids–which the body cannot produce in sufficient quantities–must be obtained through food. Amino acids from dietary protein provide the raw materials needed to synthesise hormones and other proteins involved in endocrine function.
The amino acid pool is a dynamic supply of free amino acids in the blood and tissues. It is typically replenished by dietary protein breakdown, the breakdown and recycling of existing body proteins, and the body's synthesis of non-essential amino acids. Cells use these amino acids to build specific proteins through transcription, in which DNA instructions are copied into messenger RNA (mRNA), and translation, in which ribosomes read the mRNA instructions and link amino acids together using peptide bonds.
Some hormones are made from amino acids, either by modifying a single amino acid or by joining several amino acids into chains through protein synthesis. For instance, insulin, produced by the pancreas, is a protein hormone that helps regulate blood glucose. Insulin-like growth factor 1 (IGF-1), which supports growth and tissue repair, and thyroid-stimulating hormone (TSH), which signals the thyroid gland to produce thyroid hormones, are also protein-based hormones.
A well-oiled transport system
Hormones need to travel from the organs that produce them to the tissues where they act. Certain proteins help transport them through the bloodstream. “Think of the bloodstream as a transport network. Thyroid hormones, for instance, bind to proteins such as thyroxine-binding globulin. Steroid hormones, including oestrogen, testosterone and cortisol, also circulate mostly bound to transport proteins,” says Dr. Janani.
Transport proteins influence how hormones circulate and how long they remain in the bloodstream.
These transport proteins influence how hormones circulate and how long they remain in the bloodstream. Since the body synthesises these proteins using amino acids, adequate protein intake contributes to their production.
“When protein and overall food intake are inadequate for a prolonged period, we may see loss of muscle, reduced strength, poor growth in children, slower recovery from illness, and, in case of severe malnutrition, swelling of the feet or legs and changes in hair or skin,” says Dr. Sakthivel Sivasubramanian, Consultant Endocrinologist and Lifestyle Physician at The Hormone Clinic, Tiruchirappalli.
Also read: Is your body low on protein? Signs and impacts of a deficiency
Protein as sidekick
The body must also activate and process hormones once they are transported and reach their target cells or tissues–so the hormones can perform their functions. The thyroid gland produces mainly thyroxine (T4), which is converted into triiodothyronine (T3), the more biologically active form in many tissues. T3 helps regulate metabolism and body temperature.
“This conversion depends on enzymes called deiodinases, which are proteins that require selenium to function properly. Amino acids from dietary protein help the body produce these enzymes, making adequate nutrition important for normal thyroid hormone activity,” notes Dr. Janani.
Blood sugar and appetite
Protein also plays a key role in blood glucose regulation by slowing carbohydrate digestion, stimulating the release of insulin and hormones such as GLP-1, and providing amino acids that the body can gradually convert into glucose without causing a sharp blood sugar spike. “Think of protein as a speed breaker,” explains Dr. Janani. A balanced meal containing protein, carbohydrates and fibre can moderate the rise in blood glucose after eating. Insulin and glucagon, two hormones produced by the pancreas, regulate blood glucose. Insulin helps glucose move into cells, while glucagon helps make glucose available to the body between meals.
Think of protein as a speed breaker.
Amino acids from protein-containing meals can stimulate the release of both. Consuming protein increases amino acid levels in the blood, stimulating pancreatic beta cells to release insulin and alpha cells to release glucagon. Insulin helps the muscles use amino acids to build tissue, while glucagon signals the liver to convert excess amino acids into glucose, thus preventing blood sugar levels from dropping too low.
Protein also influences appetite-regulating signals. Ghrelin, often called the hunger hormone, signals the brain when it is time to eat. Leptin, produced mainly by fat cells, regulates the body’s energy balance and appetite in the long term. “A protein-rich meal tends to lower ghrelin and raise fullness signals (an indication of satiety) such as GLP-1 (glucagon-like peptide-1) and PYY (peptide YY). This is one reason why meals such as eggs with wholegrain toast, or dal with rice and vegetables may keep us satiated for longer than a meal consisting largely of refined carbohydrates,” says Dr. Janani.
“The overall response depends on a balanced meal and the person's health; it is not as simple as ‘the more the protein, the better the blood sugar’,” notes Dr. Sakthivel.
Also read: Protein’s seen and unseen benefits: How it affects metabolism, muscle repair
Mood and sleep
Protein also supplies amino acids involved in processes that influence mood and sleep. One example is tryptophan, an essential amino acid that the body uses to produce serotonin, a neurotransmitter involved in mood regulation. Serotonin is also a precursor to melatonin, the hormone that helps regulate the sleep-wake cycle.
Adequate protein intake supplies the amino acids needed for these processes, although mood and sleep are also shaped by factors such as stress, physical activity and light exposure (light regulates your body’s internal clock, or circadian rhythm. While protein provides amino acids like tryptophan to make brain chemicals, light helps regulate the timing of processes such as melatonin production and sleep).
Reproductive health and menstrual function
Reproductive health depends, among other things, on communication between the brain and reproductive organs, coordinated through a network of hormones. In women, follicle-stimulating hormone (FSH) and luteinising hormone (LH), both produced by the pituitary gland, help regulate ovarian function, including follicular development and ovulation. These protein-based hormones form part of the hypothalamic-pituitary-ovarian axis, which coordinates signals between the brain and ovaries.
Oestrogen and progesterone, meanwhile, are steroid hormones made from cholesterol rather than directly from dietary protein. However, the enzymes involved in their synthesis–such as aromatase, which helps convert androgens into oestrogens, and 3β-hydroxysteroid dehydrogenase, which helps produce progesterone–are proteins. Transport proteins, such as sex hormone-binding globulin and albumin, also help carry these hormones through the bloodstream.
Very low protein intake, especially when the body does not get enough energy from food, can disrupt hormonal signalling between the brain and ovaries, potentially contributing to irregular or missed periods, says Dr. Janani. However, menstrual irregularities can have several causes, including stress, excessive exercise, pregnancy and underlying medical conditions. They should not automatically be attributed to protein deficiency.
Also read: Why your body may not be optimising the protein you eat
Protein is not a lone superhero
A national survey done by ICMR–INDIAB reveals that the typical Indian diet derives a massive 62.3% of its energy from low-quality carbohydrates and only 12% from protein. While studies have established the metabolic links between protein and macronutrient imbalances and disruptions to insulin, thyroid function, and satiety signaling, experts have said that a well-balanced diet along with other factors play a role in hormonal imbalance.
"Consuming adequate protein is just a part of the puzzle as overall health status, nutrition intake, sleep, lifestyle and stress also matter when it comes to hormone balance, supporting immunity, managing mood or supporting reproductive health," notes Aditi Prabhu, a nutritionist.
Although protein supports normal hormonal function, inadequate protein intake is only one of several factors that can cause it. Fatigue, weakness and other symptoms may also be associated with nutritional deficiencies, stress or underlying medical conditions.
Consuming adequate protein is just a part of the puzzle as overall health status, nutrition intake, sleep, lifestyle and stress also matter.
“The body can often maintain hormone production despite variations in protein intake, and symptoms of protein deficiency usually overlap with those of other nutritional deficiencies and illnesses,” says Dr. Kavitha Muniraj, Medical Director, Senior Consultant - Endocrinology, Samatvam Diabetes Centre, Bengaluru.
Severe protein deficiency, particularly when accompanied by inadequate calorie intake, can interfere with normal growth and metabolism. “For instance, prolonged undernutrition can lower IGF-1 levels, even when the growth hormone is present,” Dr. Kavitha explains.
Increasing protein intake is not a treatment for thyroid disease, diabetes or other endocrine disorders. “The goal is adequate protein, not automatically a high-protein diet,” notes Dr. Sakthivel.
Cover art by Pratik Bhide