What are the factors that lead to weight gain?


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There are many triggers of weight gain, but at the physiological level in our bodies, those triggers narrow down to common weight gain pathways.

(i) Hormonal Pathway

In this pathway, hormonal imbalances or deficiencies contribute to weight gain. Hypothyroidism (insufficient amounts of thyroid hormones) is one example. The thyroid hormone is an important natural metabolism booster.

Point to note:Metabolism refers to the whole range of biochemical processes in the body that support life. There are two forms: anabolic (synthesis of chemicals such as other enzymes etc) and catabolic (breakdown of chemicals such as fats and starch etc). There are various hormones that regulate metabolism. In addition, hormones have unique feedback mechanisms that regulate their actions. Hormones regulate each other.

If the thyroid hormone is absent or insufficient, metabolism slows down. Hypothyroidism can occur in all sexes and ages but is common in older women. As women age, their thyroid hormone levels may reduce thus compromising their metabolic power. This condition is normally treated with daily hormone-replacement tablets such as levothyroxine.

Secondly, reproductive hormones imbalances (estrogen and testosterone) which are caused by polycystic ovary syndrome (PCOS) (overproduction of the male hormone testosterone in females) are another example. This leads to low estrogen levels which in turn impair insulin

functions. Under normal circumstances, estrogen boosts the activity of insulin. Insulin helps regulate sugar (glucose) levels in the blood. It is vital to note that fats, starches, and proteins in foods are converted into glucose (sugar) depending on the needs of the body. The glucose is used to generate energy (ATP) that is needed by the body for normal functioning. Insulin helps trigger the conversion of glucose into energy. When it has malfunctioned, glucose levels in the blood rise rapidly which is, in turn, converted into fats in the adipose tissues and not energy leading to weight gain.

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In addition, progesterone is produced naturally in the ovaries and it helps regulate menstrual cycle and pregnancy. Progesterone and estrogen must be in balance. Stress, menopause, and some birth control pills may cause estrogen-progesterone imbalances. If the imbalance affects estrogen levels, insulin’s activity is derailed as explained earlier.

Leptin is another hormone which plays a crucial role to signal the body to stop further consumption of food. Its presence shows the body has enough calories. Overconsumption of sugary foods such as candies, chocolates, and processed foods may inhibit the functions of leptin thus allowing overeating and generation of excess calories that are converted into fats which in turn lead to weight gain. Leptin’s actions are countered by Ghrelin, an appetite-stimulating hormone (encourages food cravings) which in turns leads to excess calorie production. The excess calories are converted into fats leading to weight gain. Stress, depression and certain medications may trigger the effects of ghrelin.

Stress may also lead to the overproduction of Cortisol. When one is stressed, Cortisol triggers glucose (sugar) production which is converted into fats thus contributing to weight gain. Managing stress will normalize Cortisol production thus regulate sugar levels.

In addition, melatonin is secreted by the pineal gland that helps maintain the circadian cycle (sleep and wake cycle). Melatonin levels rise in the evening and in the night but subside early in the morning. During sleep, this hormone triggers growth and development, body healing, an increase in bone density, and building of lean muscle. Lack of sufficient sleep triggers production of stress hormones which in turn cause weight gain as explained earlier.

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Besides, glucocorticoids are secreted to counter inflammation and they are accompanied by mobilization of glucose from fats and proteins (increase in blood glucose). Chronic inflammation leads to increased Glucocorticoids production thus increased sugar levels that are eventually converted into fats thus causing weight gain. Stress can lead to an increase in the levels of Glucocorticoids.

Point to note: stress may trigger the production of hunger hormones (food cravings) in some people. In others, it may trigger production of stress hormones such as Cortisol and Glucocorticoids which initiate glucose production. Excess glucose may be converted into fats.

Table 1: Summary of Hormonal Pathway.

  Hormone Effect
oLOW EstrogenImpaired insulin actions
oHIGH ProgesteroneLow estrogen levels and impaired
  insulin actions
oLow Insulin/InsulinImpaired conversion of glucose to
 insensitivityenergy. In turn, excess glucose is
  converted into fats.
oLOW or insensitiveImpaired hunger regulation.
oHIGH GhrelinImpaired hunger regulation.
oHIGH CortisolIncreased food cravings.
oHIGH GlucocorticoidsIncreased glucose production. This
  leads to the storage of excess glucose
  as fats.  
oLOW MelatoninLack of sleep (insomnia) and
  consequently, a rise in stress
Hormonal effects

(b) Reduction in Metabolism or Insufficient Metabolism Pathway

Aging, lack of exercise, and hypothyroidism are the three main causes of a reduction in metabolism. Naturally, the rate of metabolism slows down as people age. Aging is characterized by changes in body composition. CT studies demonstrate that as we age, subcutaneous fat (below the skin, SF) decreases and visceral fat (in the abdominal cavity, VF) increases. VF is the enemy. Because it causes systemic inflammation, it is an independent risk factor for coronary artery disease, stroke, and death. If that’s not enough, VF also provides the Buddha-belly mid-life midriff.

The other most common age-related change in body composition is muscle loss. Because muscle has a high metabolic rate, its loss is associated with a reduction in energy expenditure. This decrease in caloric burn lends itself to weight (fat) gain.

Both increased VF and decreased muscle mass are linked to a loss of insulin sensitivity which leads to poor conversion of glucose to energy (and in-turn leads to conversion of the excess glucose into fats).

No one needs to be reminded of the benefits of regular exercises. Exercise helps to burn fats (calories) as well as promotes the growth of lean muscle. A balanced diet rich in fruits and vegetables slows the rate of aging.  

(c) Underlying Medical Conditions Pathway
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Chronic inflammation, stress (depression and anxiety) polycystic ovary syndrome (PCOS) and hypothyroidism have been explained in detail at the hormonal pathway level.

Fluid retention is another cause. Medically referred to as edema, this accumulation of fluid under the surface of the skin between areas of tissue or in one of the body’s organs is extremely common, especially in the feet and lower legs. While in some cases it can simply be a short-term symptom of standing up all day, it can also be a signifier of a more serious medical condition.  Weight gain is just one of the symptoms of edema, with soreness of the muscles, joints, and limbs, and changes in the color of the skin being among others. The condition known as pitting edema leaves an indentation after applying pressure to the affected area.

Edema can be a symptom of pregnancy, or a disease of one of the internal organs, such as the heart, liver or kidneys. It is also a side effect of oral contraceptives, corticosteroids, and medicine for high blood pressure.

The symptoms of fluid retention often clear up on their own, but if they persist you should see you doctor to check that it is not part of an underlying health issue. They may prescribe medication and also suggest some lifestyle changes such as changing your diet or taking more exercise.

(d) Use of Certain Drugs/Medications Pathway

Certain birth control pills and synthetic steroid hormones lead to affect the levels of estrogen which as we have seen under the hormonal pathway leads to weight gain.

Other drugs that may cause medicine-related weight gain include:

Drugs for diabetes, such as insulin, thiazolidinediones, and sulfonylureas.

Antipsychotic drugs such as haloperidol, clozapine, and lithium.

Antidepressant drugs like amitriptyline, paroxetine, and sertraline.

Drugs for epilepsy like valproate and carbamazepine.

Steroid hormone drugs like prednisone or birth control pills.

Blood pressure-reducing drugs like beta-blockers.

  • Genetics Pathway

Everyone knows some people who can eat ice cream, cake, and whatever else they want and still not gain weight. At the other extreme are people who seem to gain weight no matter how little they eat. Why? What are the causes of obesity? What allows one person to remain thin without effort but demands that another struggle to avoid gaining weight or regaining the pounds he or she has lost previously?

On a very simple level, your weight depends on the number of calories you consume, how many of those calories you store, and how many you burn up. But each of these factors is influenced by a combination of genes and the environment. Both can affect your physiology (such as how fast you burn calories) as well as your behavior (the types of foods you choose to eat, for instance). The interplay between all these factors begins at the moment of your conception and continues throughout your life.

Genetic influences

To date, more than 400 different genes have been implicated in the causes of overweight or obesity, although only a handful appear to be major players. Genes contribute to obesity in many ways, by affecting appetite, satiety (the sense of fullness), metabolism, food cravings, body-fat distribution, and the tendency to use eating as a way to cope with stress.

The strength of the genetic influence on weight disorders varies quite a bit from person to person. Research suggests that for some people, genes account for just 25% of the predisposition to be overweight, while for others the genetic influence is as high as 70% to 80%. Having a rough idea of how large role genes play in your weight may be helpful in terms of treating your weight problems.

How much of your weight depends on your genes?

Genes are probably a significant contributor to your obesity if you have most or all of the following characteristics:

You have been overweight for much of your life.

One or both of your parents or several other blood relatives are significantly overweight. If both of your parents have obesity, your likelihood of developing obesity is as high as 80%.

You can’t lose weight even when you increase your physical activity and stick to a low-calorie diet for many months.

Genes are probably a lower contributor for you if you have most or all of the following characteristics:

You are strongly influenced by the availability of food.

You are moderately overweight, but you can lose weight when you follow a reasonable diet and exercise program.

You regain lost weight during the holiday season, after changing your eating or exercise habits, or at times when you experience psychological or social problems.

These circumstances suggest that you have a genetic predisposition to be heavy, but it’s not so great that you can’t overcome it with some effort.

At the other end of the spectrum, you can assume that your genetic predisposition to obesity is modest if your weight is normal and doesn’t increase even when you regularly indulge in high-calorie foods and rarely exercise.

People with only a moderate genetic predisposition to be overweight have a good chance of losing weight on their own by eating fewer calories and getting more vigorous exercise more often. These people are more likely to be able to maintain this lower weight.

People with a strong genetic predisposition to obesity may not be able to lose weight with the usual forms of diet and exercise therapy. Even if they lose weight, they are less likely to maintain weight loss. For people with a very strong genetic predisposition, sheer willpower is

ineffective in counteracting their tendency to be overweight. Typically, these people can maintain weight loss only under a doctor’s guidance. They are also the most likely to require weight-loss drugs or surgery.

(f) Pregnancy Pathway

Weight gain is common during pregnancy because the body has to accommodate the growth of the baby. This can be as a result of increased eating and an increase in growth hormones and processes. However, these triggers often subside after delivery but for some, weight gained during pregnancy may persist.

Where Does the Extra Weight Go During Pregnancy?

Baby: 8 pounds

Placenta: 2-3 pounds

Amniotic Fluid: 2-3 pounds

Breast tissue: 2-3 pounds

Blood supply: 4 pounds

Stored fat for delivery and breastfeeding: 5-9 pounds

Larger uterus: 2-5 pounds

Total: 25-35 pounds

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