Weight Loss Calculator

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This weight loss calculator provides guidelines for weight loss by estimating basal metabolic rate and using the principle of calories in and calories out to determine the number of calories a person should consume to meet their weight loss goals. The calorie needs of a person is estimated using the Mifflin-St Jeor Equation, which is based on the age, sex, height, weight, and activity level of the person. Please reference the Calorie Calculator to understand how it is estimated. The primary result of this calculator is the number of calories you should consume for your weight loss plan. You can click the "view macro" link to see the recommended macronutrient intake amount for the day based on the calorie amount. This calculator is intended for adults between the ages of 18 and 80 years old.


Body weight and health

A person's body weight can have a significant impact on their health. Being underweight or overweight both have their own health risks, so it is important to have a doctor assess your body weight as well perform other health assessments periodically to evaluate your risk of disease (or diagnose the status of a disease) if your weight is not within a range that is considered normal for your circumstances.

Risks associated with being overweight/obese:

Excess weight, particularly obesity, has a detrimental effect on almost all aspects of health. Overweight/obesity can occur as a result of excessive food intake, imbalanced diet, genetics, lack of exercise, stress, medications, environment, and more. It increases the risk of many diseases such as diabetes, heart disease, certain cancers, and more. It decreases a person's overall quality of life as well as longevity, and can also result in depression and social isolation. Some of the adverse effects of overweight/obesity are detailed below:

  • Heart disease and stroke: obesity increases the likelihood of a person having high blood pressure and cholesterol levels, which in turn increase the risk of adverse events such as heart attacks and strokes.
  • Type 2 diabetes: type 2 diabetes affects the body's interaction with insulin, which lessens its ability to regulate blood sugar and increases the risk of many health issues like heart disease and stroke. It can also result in adverse effects such as blindness, kidney failure, and amputation.
  • Sleep apnea: a person with sleep apnea may momentarily stop breathing during sleep, which reduces the quality of sleep. Those who are overweight or obese have an increased risk of sleep apnea due to the larger amount of fat stored around the neck which causes the narrowing of the airways.
  • Cancer: the risk of certain cancers is increased by overweight/obesity, including cancer of the cervix, uterus, breast, colon, esophagus, rectum, pancreas, kidney, prostate, and more.
  • Depression: Many of those affected by obesity experience depression, often as a result of discrimination based on their body size that over time affects their self-worth. This in turn can lead to those affected isolating themselves, compounding the issue.

Although BMI is an imperfect measure, it is useful as a screening tool to determine whether further assessment is necessary. On average, a person is considered to have a normal weight if they have a BMI of 18.5-24.9. Those who have a BMI between 25.0 and 29.9 are considered overweight, and those with a BMI ≥ 30 are considered to be obese. For those who fall within the range of overweight/obese, it is likely worth a visit to the doctor to determine whether any intervention is necessary.

Risks associated with being underweight:

Like overweight/obese, being underweight can also have detrimental health effects. Underweight can be caused by a variety of factors such as genetics, faulty metabolism, lack of food, drugs, illnesses (physical or mental), and eating disorders such as anorexia nervosa. Some of the adverse effects of underweight are detailed below:

  • Malnutrition: being underweight often corresponds to insufficient nutrient intake. If the body doesn't get the nutrients it needs, over time, it results in symptoms such as lack of energy, feeling tired, getting sick often and taking longer to recover, hair thinning/loss, and for women, irregular or skipped periods.
  • Decreased immune function: some studies have shown that those who are underweight are more prone to infections, but these studies also question whether this is due to the underlying factors causing the person to be underweight rather than the state of being underweight.
  • Osteoporosis: underweight has been shown to be correlated with low bone mineral density and osteoporosis.
  • Infertility: Underweight women have an increased risk of irregular or missed menstrual cycles, and may also not ovulate. A woman who chronically does not ovulate is at risk of infertility.
  • Developmental delays: children who are underweight, particularly as a result of malnutrition, are at high risk of developmental delays. A child's body needs nutrients for proper brain development. A child who does not consume sufficient nutrients may experience inadequate brain development that in turn leads to delays in developmental milestones.

Although BMI is an imperfect measure, it is useful as a screening tool to determine whether further assessment is necessary. On average, a person is considered to have a normal weight if they have a BMI of 18.5-24.9. Those who have a BMI between 17.0-18.4, 16.0-16.9, and < 16.0 are considered to be mildly, moderately, or severely underweight, respectively. For those whose BMI is below 18.4, it may be worth visiting a doctor to determine whether any intervention is necessary.

Calorie counting for weight loss

One of the most well-known and widely used weight-loss methods involves counting calories. The method is often abbreviated as CICO (calories in calories out) to emphasize the basic idea that if we consume more calories than we burn, we will gain weight. If instead we burn more calories than we consume, we will lose weight.

Thus, the method focuses on determining your basal metabolic rate (BMR). This is the amount of calories we burn in a day at rest based on our metabolism. We would burn this amount regardless of what we do throughout the day. BMR is based on a number of factors such as age, lean body mass, muscle mass, aerobic fitness level, and more. It is calculated using a variety of different formulas that won't be explained here. Essentially, the concept of CICO is formed on the basis that as long as fewer calories are consumed than burned during the day, we will lose weight. Similarly, if the amount consumed is higher than the amount burned, we will gain weight. If the amount is equal, we will maintain our weight. The above of course assumes the absence of any complicating factors such as disease, genetics, etc.

It is a relatively simple weight-loss method in concept, but requires some estimation to determine BMR. Also, this method does not account for the types of foods consumed. While the most important factor is weight-loss, it is possible to gain/lose weight while eating unhealthy foods, and following this method of weight loss does not necessarily guarantee health if the foods being consumed to meet caloric goals are bad for your overall health.

Alternative weight loss methods

CICO is not the only scientifically backed weight-loss method that works. Some others include intermittent fasting and mindful eating.

Intermittent fasting:

Intermittent fasting (IF) involves limiting eating to very specific periods of time, alternating between fasting and not fasting. It can have a similar effect to restricting calories in regards to weight loss and reducing the risk of diet-related diseases. There are several methods used in intermittent fasting:

  • Alternate day fasting: this involves fasting every other day while eating normally on days when you are not fasting.
    • Complete alternate-day fasting - no calories are consumed on fasting days.
    • Modified alternate-day fasting - on fasting days, a person may eat ~25-30% of the body's energy needs within a limited timeframe. There are no restrictions on non-fasting days.
  • 5:2 diet: this diet involves fasting 2 out of every 7 days. On the two fasting days, ~25% of daily caloric needs are consumed. There are no restrictions on the non-fasting days.
  • 16/8 method: this involves fasting for 16 hours out of every day, and only eating during an 8-hour window. There are no restrictions on the number of calories a person can consume during this 8-hour window. Despite the lack of restrictions, studies have shown that those who adhere to eating only within this window consume fewer calories over the period and tend to lose weight.

Mindful eating:

Mindful eating is the practice of being attentive about what you consume. Most people lead busy lives, and the things they choose to eat are often a result of convenience or necessity rather than preference. In other cases, people may simply not be aware of how much they actually consume on a daily basis, often forgetting snacks they may have had outside of mealtimes. Mindful eating seeks to form better eating habits that ensure a person is aware of all that they consume in the hopes that being fully aware reduces excessive or unhealthy consumption. When people are truly aware of what they are consuming, they tend to better regulate what they eat and are more likely to be able to lose weight, should that be the goal. Below are some tips for mindful eating:

  • Sit down to eat at a table, avoid distractions by paying attention to the food being consumed, and eat slowly. Taking time to eat slowly allows the brain to process what is being eaten and signal when you are full. The fact that it takes time for the brain to process is what sometimes leads to feeling excessively full if we eat too quickly. Being mindful of this can help prevent over-eating, thereby resulting in weight loss.
  • Be mindful of the kinds of calories being consumed, as it can have a significant impact on weight loss. Consuming protein and fiber-rich foods contributes to feelings of fullness for longer periods of time thereby providing more benefit per calorie consumed. On the other hand, foods such as heavily refined carbohydrates and sugar do not contribute much to feelings of fullness while also being calorie heavy and providing little in terms of nutrition.
  • Be mindful of what you eat when you are stressed. Chronic stress triggers the release of hormones that increase appetite so it is especially important to be aware of what and how much you choose to eat when stressed. If the stress is causing overeating, alleviating the stress may be enough to result in significant weight loss.
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