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Does T3 Help You Lose Weight? Find out...

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T3 is one of the two major hormones released from the thyroid. It is also the more important one because it is more potent than T4. Therefore, T3 level is crucial to the metabolic rate of the body and the metabolic rate can determine weight. However, there is a third thyroid hormone that blocks the effects of T3. Read on to find out how important T3 is to your weight loss plans and how it can help you shed weight.

How T3 Can Promote Weight Loss

The only mechanism by which T3 promotes weight loss is by increasing metabolic rate.

Although it is a one-trick weight loss solution, that one trick is pretty remarkable. T3 increases the basal metabolic rate by increasing the rate at which the body breaks down all food groups. It unlocks significant energy for the body to use, and it can produce very dramatic results especially in overweight people with diagnosed or silent hypothyroidism.

When the amount of thyroid hormones produced in the body falls, the rate of metabolism falls with it. In this regard, the amount of circulating T3 is more important than that of T4.

Because of the reduced metabolic rate, low thyroid functioning results in difficulty in reducing body weight. When overweight individuals adopt healthy, low-calorie diets and take up regular exercise but still cannot shed weight, the most likely reason is a low metabolic rate caused by low T3 levels.

Even a 10% reduction in metabolic rate can make weight loss very difficult. However, available clinical data suggest that most people who find it difficult to lose weight have a 15 – 40% reduction in metabolic rate.

For this group of people, T3 is the magic remedy for losing weight.

The ability of T3 to promote weight loss does not really depend on adopting a low-calorie diet. In fact, the usual response to a low-carbohydrate diet is a reduction in the body’s metabolic rate. By supplementing with T3, the body keeps up a high rate of metabolism even with the number of calories in the diet is reduced.

Exercise, on the other hand, has a more significant effect on the result of T3 supplementation in weight loss. In fact, T3 increases the amount of available energy and practically encourages the user to exercise.

Unlike stimulants like caffeine and synephrine, T3 increases the rate of metabolism without such side effects as jitters. It does not make the user “hyper”. Instead, it simply energizes the user without the crash that comes from overstimulation with stimulants.

When taking T3 for weight loss, the aim is to increase the levels of T3 to the edge of the upper limit while not stepping over and setting off hyperthyroidism.

To do that, it is important to closely monitor the plasma levels of T3 while taking the supplement.

Where this is not possible, clear signs of hyperthyroidism such as irregular, rapid heartbeats should be the indication to stop T3 supplementation.

In most cases of abnormal weight gain even in the face of dieting and exercise, there is an impairment in the enzymes responsible for converting T4 to T3. Since most of the circulating T3 in the body comes from T4, such impairment makes it important to find another source of T3. This can be done with drugs and supplements that increase T3 levels.

What is T3?

T3 is also known as triiodothyronine, a thyroid hormone. It is related to another thyroid hormone, T4, or thyroxine.

Thyroxine is the precursor of T4 and the production of both hormones is signaled in the thyroid gland by TSH or thyroid-stimulating hormone.

The thyroid-stimulating hormone is released from the pituitary gland and forms a feedback loop with both T3 and T4. Therefore, when the plasma levels of the thyroid hormone fall, TSH production is increased, and when the thyroid hormones rise above their normal plasma levels, TSH production is reduced.

The control over the release of TSH itself is found in the thyrotropin-releasing hormone (TRH) which is released from the hypothalamus.

T3 is only 20% of the number of thyroid hormones synthesized. The other 80% is thyroxine.

However, in the plasma, T3 is only 2.5% of the circulating thyroid hormones. It does not last as long as thyroxine (the time taken for T3 concentration to reduce to half is 2.5 days while for T4, that time is 6.5 days).

Furthermore, most of the T3 found in circulation is produced from T4.

By simply removing an iodine atom in a specific position on the T4 molecule, T3 is produced. The enzymes responsible for converting T4 to T3 are found in different parts of the body including the thyroid, kidney, liver, adipose tissue, placenta, heart, central nervous system, and even the pituitary gland.

Even though T3 can be made from T4, the body still makes triiodothyronine directly. This is done in the lumen of the thyroid gland.

The synthesis proceeds with the addition of iodine atoms to tyrosine to form monoiodotyrosine (MIT) and diiodotyrosine (DIT). These reactions require hydrogen peroxide to proceed.

MIT and DIT then combine in a reaction catalyzed by an enzyme called thyroid peroxidase. The product of this combination is T3.

What T3 Does and How It Works

The biological effects of T3 are extensive and the hormone contributes to almost all the physiological processes in the human body. For example, T3 affects heart rate, the rate of metabolism, body temperature, and growth rate.

In the blood, T3 binds to specific types of carrier proteins: serum albumin (with low affinity) and thyroid-binding globulin (with high affinity).

These molecules increase the stability and longevity of T3 but impede the uptake of the hormone by tissues. For T3 to pass through tissues, it must shed its carrier protein.

To produce its biological effects, T3 binds to thyroid receptors in tissues. Also, because it is fat-soluble, it can cross into cells through their phospholipid layers.

T3 can be found in most tissues although it is notably absent in the tissues of the testes and spleen.

Its overall effect depends on the part of the body where it acts. However, T3 generally increases the basal metabolic rate.

When T3 increases the rate of metabolism, it does the following:

  • Increase the amount of oxygen and energy used up by the body
  • Increase the number of calories required for normal body processes even when the muscles are rested
  • Increase the population of sodium/potassium/ATPase, the primary energy-generating complex in the body
  • Increase the use and breakdown of many nutrient macromolecules produced in the body

On proteins, T3 increases the rate of their production and degradation by increasing the amount of the enzymes, RNA polymerase I and II.

For carbohydrates, T3 increases gluconeogenesis. Gluconeogenesis is the production of glucose from stored glycogen. This effect is mediated by beta-adrenergic receptors. By acting on beta-adrenergic receptors, T3 can increase heart rate and pulse rate. Specifically, T3 increases systolic blood pressure but decreases diastolic blood pressure.

On lipids, T3 increases the rate of lipolysis. Specifically, it drives the breakdown of cholesterol and increases the number of LDL receptors.

In the brain, T3 increases the production of certain neurotransmitters especially serotonin.

The positive effect of T3 on serotonin is the reason it is now recommended (along with SSRIs or selective serotonin receptor inhibitors) in the treatment of drug-resistance and recurring depression and bipolar disorders. Different studies have established that long-term supplementation with T3 significantly improves the symptoms of (and may even “cure”) these psychological disorders.

T3 (or any of its prodrugs) is also used as a fat loss supplement. It has been proven to increase the metabolism of fatty acid and the breakdown of fat stored in adipose tissue

Reverse T3: The Dark Brother of T3

Although it is a well-known fact that the conversion of T4 to T3 actually produces two kinds of T3, only recently has the biological importance of this knowledge been applied to weight loss.

T4 is converted to a bioactive T3 and reverse T3. Scientists used to believe that reverse T3 is an inactive metabolite but new evidence proves that that is not really the case.

Reverse T3 has none of the effects of T3 on metabolic rate. Instead, it actually reduces the metabolic rate.

Therefore, reverse T3 is not a dud metabolite of T4 (or a useless twin of T3) as it was described in the past. Rather, it blocks the effects of T3 and is, therefore, an anti-thyroid hormone.

When the amount of freely circulating T3 is low, the amount of reverse T3 rises, and vice versa. This means that high levels of reverse T3 can also be taken as a sign of hypothyroidism, reduced metabolic rate, and difficulty shedding weight.

The body usually promotes the production of reverse T3 when it is starved and when it is experiencing chronic stress. This is the reason why dieting sometimes fails to affect weight loss. By changing one’s diet to low-calorie foods, the body recognizes it as starvation and promotes the conversion of T4 to reverse T3 instead of T3.

All of this is done to conserve the body’s store of fats and glycogen and to slow down weight loss.

Since the role of reverse T3 in weight loss is newly discovered, there is no standard recommended levels to guard against. However, clinicians who believe reverse T3 is not inactive but indeed anti-thyroid suggests 250 picograms per ml of the hormone as the limit.

Alternatively, the ratio of free T3 to reverse T3 can be used to determine when to increase T3 levels. The healthy ratio of T3 to reverse T3 is 2:1 or greater.

Studies on T3, reverse T3, and Weight Loss

The negative effect of reverse T3 on weight loss was demonstrated in a 1984 paper published in the journal, Metabolism.

In that study, researchers compared the basal metabolic rates in two groups of volunteers with similar weights. Individuals in the first group had previously experienced weight loss by dieting while those in the second group had not experienced weight loss or adopted dieting.

The results of the study showed that the basal metabolic rates of people who had lost weight by dieting were 25% lower on average than those in the second group.

The study demonstrates the lasting effect of reverse T3. Those who had used dieting to experience weight loss had increased levels of reverse T3 because their bodies ramped up the production of the anti-thyroid hormone when faced with starvation. This led to a significant reduction of the basal metabolic rate which makes it difficult for such people to lose more weight or for them to shed weight at all if they ever regained the lost weight.

The link between T3 and weight loss is far from new. As far back as 1976, a study published in the journal, The Lancet, demonstrated serum T3 levels are positively correlated with body weight.

The study found out that overeating increases T3 levels in healthy individuals to promote weight loss. After weight loss, the levels of T3 then fall back to normal. A similar correlation between serum T4 levels and body weight was not observed.

A 2002 study published in the journal, Archives of Disease in Childhood agreed and disagreed with the findings of the Lancet study.

In this study, the researchers measured the levels of the hormones, T3, T4, TSH, and leptin in 118 obese children. As a control, 107 children with normal body weights had their thyroid functioning monitored too.

Thyroid hormone levels were measured in 55 of the obese children who experienced weight loss after one year on a normal energy diet. Also, these hormones were measured in 13 of the obese children who experienced no weight loss.

The study results showed that obese children had higher levels of thyroid hormones than kids with normal weight. Also, the levels of the hormones (except TSH) fell in those children who experienced weight loss.

This result suggests that the thyroid hormones are released in greater quantities in obese children to increase metabolic rate and cause weight reduction. After weight loss, the levels of these hormones are then reduced to keep the bodyweight at the normal, acceptable level.

The finding that TSH levels remain high suggests that thyroid hormones are increasingly stimulated for release. Most of the T4 produced after weight loss may be converted to reverse T3 to block the actions of T4 and T3 and then stop further weight loss.

Another study published in 2003 in the journal, Clinical Endocrinology, examined the same effects both in obese women.

The study recruited 98 obese premenopausal women and 31 non-obese women, all with normal thyroid functioning. For all these volunteers, weight, height, body mass index, body fat, fat weight, and waist circumference were all measured. The measurement was then repeated after 6 months of obesity treatment.

The study results showed that the levels of thyroid hormones and TSH were reduced in obese women who lost more than 10% of the bodyweight after the weight loss treatment.

This study goes on to show that the body can regulate the levels of thyroid hormones to promote weight loss or weight gain. However, when this regulation fails due to thyroid dysfunction, the reduced production of T3 can make weight loss difficult.





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