T3 weight loss – the science behind it

January 5, 2022by Rob Starr0

T3 is a prescription medication that can be used to help with weight loss. t3 is commonly prescribed for people who suffer from thyroid problems, but t4 and t5 are usually preferred because they are more effective in some cases. t3 has been shown to make significant improvements in the body’s ability to burn fat, which is why it’s often prescribed as part of an obesity treatment plan.

The role of metabolism

thyroid hormone levels

Your metabolism is a series of chemical reactions that break down food and convert it into the energy your body requires to function. It also influences how quickly (or slowly) your body expends calories. Genetics have a hand in determining how fast (or slowly) your metabolism operates.

You burn calories through exercise and performing normal activities. When you’re resting, your body also consumes energy. The efficiency with which it does so is known as your basal metabolic rate (BMR). Whenever you have more energy than your body requires—as a result of overeating—this energy is stored in fat cells, adding weight to your body.

The role of thyroid hormone levels thyroid hormone levels

Thyroid hormones have a significant impact on your metabolism, body temperature, and appetite control. The thyroid and the hypothalamus are two tiny regions of your brain that work together to keep both weight and energy balance in check—what’s left after you eat and what your body uses.

This isn’t exactly clear, but one thing is certain: it’s not just thyroid hormones that influence how much energy your body consumes. Thyroid hormones are only one aspect of a complicated equation; they work in tandem with numerous other hormones, proteins, nuclear receptors, and chemicals.


Thyroid hormones and weight gain have been examined in many different studies, with varying results. Thyroid hormones have typically been found to be true in the obese patient as follows:

  • Thyroid-stimulating hormone (TSH) levels are either at the high end of the normal range or elevated.
  • Free T3 (triiodothyronine) levels are high.
  • Free T4 (thyroxine) levels are low.

The study concluded that the association between TSH and weight gain doesn’t necessarily mean that one causes the other. Instead, the researchers proposed that there could be a third factor involved.

However, research published in 2017 looked at 1,100 people with healthy thyroid function and found no relationship between changes in TSH and body mass index (BMI) after a ten-year follow-up. However, this study did find that those with lower amounts of free T4 had larger BMIs.

Hypothyroidism and weight

thyroid hormone levels

As previously said, the basic explanation is that when people have an underactive thyroid, their bodies stop burning calories effectively, causing them to gain weight. The majority of this extra weight is water and salt. Typically, the more severe the hypothyroidism is, the greater the amount of weight gained, but it’s generally between five and ten pounds.

Autoimmune hypothyroidism affects 10% to 60% of obese persons. Some research have shown that even mild thyroid disease might contribute to weight gain and changes in BMI, according to certain studies.

Weight loss with treatmentthyroid hormone levels

There are no scientific studies on how much weight is gained or lost when hypothyroid patients are treated with levothyroxine, but the limited evidence that is available suggests that not everyone loses weight and in those who do, it’s modest.

Once your hormones are in the normal range, you may lose a little weight—mainly water and salt—as a result of all the extra water and salt your body has stored up. However, weight gain is multifactorial, and yours is most likely not due to your thyroid slowing down. If therapy has alleviated all of your other thyroid symptoms but not your weight increase, this indicates that your thyroid isn’t the only reason for it.

The weight loss challenge

thyroid hormone levels

Losing weight is a difficult task for anyone, but it can be much more so when you have hypothyroidism. Low T3 levels and hormone resistance issues may play a role in why this is the case. In some situations, understanding how much to eat and speaking about the best foods with a dietitian or nutritionist might be a useful first step.

Low t3 Levels

When your metabolism is slowed, you must consume less food and exercise more to burn calories so that your current body weight or weight does not change. This can make losing weight difficult. Lower T3 levels are connected with decreased resting metabolic rates. As previously stated, when your metabolism is slower, you’ll need to eat less and exercise more to preserve your present weight.

Hormone resistance

Another probable cause of the weight loss struggle is leptin resistance and insulin resistance, which are both linked to thyroid disease.

Leptin Resistance

Leptin is a hormone produced by your fat cells that regulate energy balance and metabolism. Leptin also signals the hypothalamus when you’ve had enough to eat, prompting thyroid hormone production to burn fat.

Leptin resistance occurs when there is too much leptin, which happens when you are overweight.7 When your hypothalamus isn’t being adequately informed that you’re full, it goes into starvation mode and tells you that you’re still hungry because your hypothalamus isn’t being properly informed that you’re satisfied.

Meanwhile, your thyroid reduces your metabolism as your appetite grows and you eat more, burning fewer and fewer calories. Weight gain also causes leptin to be produced in greater amounts by fat cells.

Insulin Resistance

Insulin is a hormone made by your pancreas that keeps your blood sugar levels stable. It operates by instructing your cells to absorb extra glucose in your blood after eating and to convert it into energy.

When your cells become less responsive to the signals supplied by insulin, as they do in type 2 diabetes, your resistance to leptin increases. This makes it necessary for you to use even more insulin to keep your blood sugar levels constant. High amounts of insulin cause weight gain and raise your danger of getting type 2 diabetes.

Insulin is a fat building hormone, which boosts the amount of fatty tissue surrounding your abdominal organs and raises your risk of chronic illnesses such as type 2 diabetes. Insulin resistance develops when both hyperthyroidism and hypothyroidism are present.

What is the relationship between hypothyroidism and weight gain?

lose weight

Because the BMR in a person with hypothyroidism is reduced (see Hypothyroidism brochure), an underactive thyroid is usually linked with some weight gain. Those with more severe hypothyroidism typically gain more weight. However, the decrease in BMR caused by hypothyroidism is typically far less significant than the substantial increase seen with hyperthyroidism, resulting in lesser weight changes due to the underactive thyroid. The reason for the weight gain in hypothyroid persons is also complex, and it may not be due to fat accumulation. The majority of the extra weight acquired by hypothyroid people is caused by salt and water accumulation. Although overweightness is not common among hypothyroid individuals, it does occur. Depending on the severity of the hypothyroidism, 5-10 pounds of body weight may be attributed to the thyroid gland. Finally, if there are only one or two symptoms of hypothyroidism but no other signs, it’s less probable that the abnormal weight gain is primarily due to the thyroid gland.

Free t4

When TSH and free T4 are both low, it suggests hypothyroidism (underactive thyroid) when coupled with high T4. When compared to normal ranges, a high free T4 indicates hyperthyroidism (overactive thyroid) when paired with low TSH.

The thyroid gland’s T4, or thyroxine, is a thyroid hormone. Thyroid hormones are known as tri-iodothyronines (T3), and they have many effects in the body, including energy production and metabolism. There are two types of T4 hormones: T3 and T4.

  • Free T4: T4 hormone which is available for use by the body’s tissues
  • Bound T4: T4 hormone which is bound to a protein and can’t be used by the body’s tissues.

T4 testing is divided into two categories: functional and structural. Functional T4 tests, known as free T4 or total T4 (free T4 plus bound t4), are typically done in a lab using blood drawn from the arm or finger vein. Free T4 is the more reliable test for thyroid function.

  • The standard lab reference range for free T4 is 0.82−1.77 ng/dL.
  • For hypothyroid patients who take thyroid hormone replacement, optimal T4 levels may be in the higher half of the lab range, however, research to support this is lacking.

Free t3

Thyroid hormones T3 (triiodothyronine) and T4 have been discovered in the human body. The thyroid gland produces minor amounts of T3 (triiodothyronine) and T4, which are both thyroid hormones. Reverse T3 is a form of active thyroid hormone that can be measured, however, it is inactive T3.

Free T3 may be included in a thyroid panel, but it’s not an accurate measurement of thyroid dysfunction. Patients with low Free T3 (and high reverse T3):

  • Are usually inflamed
  • May have digestive issues
  • May be eating too few calories or too few carbs
  • May be stressed or sleeping poorly

Lab ranges:

  • The standard lab reference range for free T3 is 2.0−4.4 pg/mL.
  • For hypothyroid patients who take thyroid hormone replacement, optimal free T3 levels may be above 3 pg/mL. However, research to support this is lacking.

Low free T3 is treated with T3 medication by some practitioners. However, there are certain hazards associated with taking T3 medicine. Only after trying other therapies should a hypothyroid patient be given combination therapy with T4 and T3.

A better and more natural method focuses on the gut-thyroid connection, aiming to enhance gut health, regulate the immune system, and decrease inflammation. This can be achieved through following a healthier diet, taking high-quality probiotic supplements, reducing stress, and sleeping more often. This will frequently result in symptom resolution that would have prompted evaluation of T3 in the first place, such as tiredness or sadness.

Elevated thyroid antibodies

thyroid gland

Thyroid antibodies are not the only cause of thyroid disease. Hypothyroidism and hyperthyroidism develop in fewer than one percent of patients with elevated thyroid antibody levels.

The majority of people who were positive for TPO antibodies in the inception of a large thyroid study that followed 5,783 individuals for 9.1 years had normal thyroid function at the conclusion of the study:

  • 10.9% were overt hypothyroid
  • 3.4% were hyperthyroid
  • 62.3% had normal thyroid hormone levels

At years 3, 6, and 9, follow-up thyroid tests were performed. Subjects with TPO positivity had a 10-20% chance of developing hypothyroidism at each 3 years. Their likelihood of going hyperthyroid was less than three percent. Patients with TPO levels greater than 500 are at the greatest risk of becoming hypothyroid.

What is the thyroid gland?

thyroid gland

The thyroid gland is a butterfly-shaped endocrine gland that is generally positioned in the lower front of the neck. The thyroid’s mission is to manufacture thyroid hormones, which are secreted into the circulation and circulated throughout the body. Thyroid hormones aid the body in utilizing energy, staying warm, and maintaining the proper function of various organs such as the brain, heart, muscles, and other organs.

Can thyroid hormones help me to lose weight?

Thyroid hormones have previously been used to help people lose weight. It is doubtful that increasing or lowering thyroid hormone levels will significantly impact weight. Excess thyroid hormone treatment, according to studies, may help people lose more weight than dieting alone, but it comes with the risk of major adverse effects from the use of thyroid hormones to assist with weight loss, such as muscular protein loss, bone loss, and/or heart problems. Furthermore, after the excess thyroid hormone is discontinued, any weight reduction will almost always be regained.

Over diagnosis of hypothyroid is common

Thyroid disease is often misdiagnosed and overtreated, according to research. When interpreting thyroid hormone test results, many doctors apply a very tight range.

Up to 60% of patients may be taking thyroid hormone replacement unnecessarily, according to one fascinating research. 291 persons on Levothyroxine (Synthroid) were asked to cease treatment for 6-8 weeks in this study. Many of these people had been taking thyroid medication for many years but showed no signs of thyroid disease upon examination.

  • Patients with low thyroid function were given thyroid testing after going without synthetic thyroid hormone treatment for several weeks. 60.8 percent of patients had normal ranges, suggesting that their bodies generate enough thyroid hormone and that they do not require thyroid medication.

Although conventional and functional medicine doctors over-diagnose thyroid disease, conventional medicine typically gets it right more than functional medicine.


What is the optimal TSH level?

The optimal TSH level is speculated to fall between 0.45-0.60 mIU/L for most people, but this varies by age and gender – the lower end of the range seems more appropriate for women over 40 years old than it does in younger men or women.

How fast is weight loss with levothyroxine?

Weight loss with t replacement is gradual – on average, it takes about one to two years after starting treatment for the weight gain induced by hypothyroidism.

How much does levothyroxine increase metabolism?

Studies have found that t therapy increases basal metabolic rate by an average of about 100 kcal/day.

Does being overweight affect TSH levels?

Yes – being overweight or obese is associated with higher TSH levels, which may be because fat cells produce a hormone.

Can diet affect thyroid levels?

Yes – diet can affect thyroid levels. Some foods, like cruciferous vegetables, contain goitrogens which may interfere with thyroid function if consumed


  1. https://www.mdpi.com/1422-0067/19/7/2017
  2. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0093515
  3. https://www.thyroid.org/thyroid-and-weight/
  4. https://pubmed.ncbi.nlm.nih.gov/31481394/
  5. https://pubmed.ncbi.nlm.nih.gov/27747984/

Rob Starr

The author of the blog is a vegan, scientist and naturopath. In his blog, {Name} dispels the most popular myths about health, provides nutritional advice, makes individual menus upon request, and answers in detail the most common questions, creating a separate post for them.

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