DIE(T): SLOWER AND COLDER

Diet restriction or calorie restriction is a form of dietary intervention that involves consuming fewer calories than what is normally required for an individual's maintenance, growth, and daily activities. When an individual undergoes diet restriction, the body experiences several biological responses, including a slowdown in metabolism.

The body's response to diet restriction is an adaptation to conserve energy and promote survival during periods of food scarcity. When the body experiences a decrease in calorie intake, it responds by reducing its energy expenditure to match the lower energy intake. This response helps to maintain a balance between energy intake and expenditure and prevent excessive weight loss.

One of the ways in which the body conserves energy during diet restriction is by slowing down the metabolism. Metabolism is the process by which the body converts food into energy that is used to fuel its various functions. The body's metabolic rate is influenced by several factors, including age, sex, body size, and physical activity level.

During diet restriction, the body's metabolic rate slows down because it needs to conserve energy. The body's cells adjust their metabolic activity to reduce energy expenditure, which leads to a decrease in the body's overall metabolic rate. This decrease in metabolic rate helps the body conserve energy and prevent further weight loss.

In addition to slowing down metabolism, the body also undergoes several other responses to diet restriction, such as a decrease in body temperature, a decrease in heart rate, and a decrease in thyroid hormone levels. These responses help the body conserve energy and promote survival during periods of food scarcity.

Slow metabolism, also known as low metabolic rate, refers to a condition in which the body burns calories at a slower rate than usual. This can result in several symptoms, including:

Weight gain: When the body's metabolism is slow, it can lead to weight gain as the body burns fewer calories than it consumes.

Fatigue: Slow metabolism can cause fatigue and lethargy as the body has less energy to perform daily activities.

Cold intolerance: A slow metabolism can also lead to feeling cold more often as the body generates less heat.

Constipation: Slow metabolism can affect digestion and lead to constipation.

Dry skin and hair: A slow metabolism can reduce the production of skin and hair cells, resulting in dry skin and hair.

Poor concentration: A slow metabolism can affect cognitive function and lead to poor concentration and memory.

Mood changes: A slow metabolism can also cause mood swings and depression due to the lack of energy and hormonal imbalances.

It is important to note that many factors can affect metabolism, including age, sex, genetics, and lifestyle habits. If you experience any of these symptoms, it is important to speak with a healthcare provider to determine the underlying cause and receive appropriate treatment.

There are several methods to assess metabolic rate. Here are a few common ones:

Resting Metabolic Rate (RMR) measurement: This is a test that measures the number of calories an individual burns at rest. It involves sitting quietly for a period of time while wearing a mask that measures oxygen consumption and carbon dioxide production. The RMR measurement is considered the most accurate way to assess metabolic rate.

Indirect Calorimetry: This method estimates metabolic rate by measuring the amount of oxygen consumed and carbon dioxide produced during physical activity. This test involves wearing a mask or mouthpiece while exercising on a treadmill or stationary bike.

Bioelectrical Impedance Analysis (BIA): This method estimates metabolic rate by measuring the body's electrical impedance. BIA involves attaching electrodes to the skin and passing a small electrical current through the body.

Body Composition Analysis: This method estimates metabolic rate by measuring body composition, including muscle mass, fat mass, and bone density. This can be done using methods such as Dual-energy X-ray Absorptiometry (DXA) or bioelectrical impedance. (personally I consider DXA scans too risky for long-term health)

It is important to note that the accuracy of these methods can vary and may be affected by factors such as age, sex, and activity level. It is best to consult with a healthcare professional to determine the most appropriate method for assessing metabolic rate.

Measuring thyroid function to assess metabolic status

Temperature, pulse, and Achilles reflex are no longer typically used as primary diagnostic tools for thyroid issues, but they may provide additional information when used in conjunction with other tests and assessments.

Temperature: Thyroid hormones play a key role in regulating body temperature. Low thyroid hormone levels (hypothyroidism) can cause a decrease in body temperature, while high thyroid hormone levels (hyperthyroidism) can cause an increase in body temperature. However, other factors can also affect body temperature, such as infection, medication use, and menstrual cycle, so temperature alone is not a reliable indicator of thyroid function.

Pulse: Heart rate is often increased in hyperthyroidism due to the effects of thyroid hormones on the heart. In contrast, heart rate may be decreased in hypothyroidism. However, many factors can affect heart rate, including physical activity, stress, and medication use, so pulse alone is not a definitive indicator of thyroid function.

Achilles reflex: The Achilles reflex is a test of nerve function that involves tapping the Achilles tendon with a reflex hammer to see if the foot moves in response. Hypothyroidism can cause a slow relaxation phase of the reflex, while hyperthyroidism can cause a fast relaxation phase. However, the Achilles reflex is not specific to thyroid function and can be affected by many other factors, such as age, medications, and neurological disorders.

In summary, while temperature, pulse, and Achilles reflex may provide additional information when evaluating a patient for thyroid issues, they are not considered specific or reliable diagnostic tools on their own, equally I would not want to use a singular blood test. Diagnosis of thyroid disorders typically involves a combination of clinical evaluations, and the more information you collect they more you can understand your unique situation.

References:

• Maclean, P. S., Bergouignan, A., Cornier, M. A., & Jackman, M. R. (2011). Biology's response to dieting: the impetus for weight regain. American journal of physiology. Regulatory, integrative and comparative physiology, 301(3), R581–R600. https://doi.org/10.1152/ajpregu.00755.2010