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    It is hard to define what underweight is as some people are naturally thin and perfectly healthy. Others have underlying health problems associated with their weight. There are obviously many different reasons for being underweight and it is important to address the underlying causes.

    Possible causes

    • Eating disorders such as anorexia nervosa generally involve psychological and emotional issues that need to be dealt with.
    • Stress – can affect appetite, digestion and metabolism (the rate at which we burn up calories). It can have a huge impact on what we are able to eat in terms of time and appetite.
    • Malabsorption – can occur if we lack sufficient digestive juices to fully break down and absorb all nutrients. This can obviously affect weight. Where digestive symptoms are present bowel disorders should be ruled out or dealt with (crohns, diverticulitis and colitis).
    • Parasites – an imbalance in the gut bacteria can affect digestion and absorption and can lead to weight loss.
    • Compromised liver function – the liver plays a big role in the digestion of protein, carbohydrates and fats. If the liver is struggling with its load the digestion and absorption of these macronutrients will be compromised.
    • Overactive thyroid – the thyroid controls our metabolic rate. If it is overactive calories will be burnt up faster than normal and weight loss is likely. Other symptoms include feeling hot, insomnia, irritability, nervousness, increased bowel movements and fewer or lighter periods.
    • Food allergies, intolerances and celiac disease – these can all affect digestion and absorption and should be investigated.
    • Serious illness – any sudden or dramatic weight loss should prompt investigation into potential underlying causes. Diabetes, AIDS, cancer and trauma can all cause dramatic weight loss.
    • Medical treatments – chemotherapy, radiotherapy and surgery may all cause weight loss and loss of appetite.

    So if you are underweight with none of the adverse reasons outlined above and wish to increase your weight,  you must be eating more calories (energy) than you are expending. Energy in (calories in) must be greater than energy out (calories out.) Below are examples and explanations of how the body puts ‘Energy In’ and puts ‘Energy Out:’

    Energy in: This refers to any food or drink which contains calories/energy.

    Energy Out: This refers to ways in which energy is expended in the body, this occurs in 3 ways:

    (1) Through the movement of your body. Any movement produced by your body requires energy, a general rule of thumb is the more muscle fibres used to move the more calories you will be using or ‘burning’. Running on a treadmill burns more calories than cycling on a gym bike since the gym bike only requires the leg muscles to move, whereas running requires muscles throughout the entire body to work.

    (2) Through the digesting of your food. Eating and digestion of food will result in ‘energy out.’ You are expending energy and burning calories when eating.

    (3) Through simply keeping alive. Your body burns calories even when you are doing nothing. This is known as your Basal Metabolic rate and is the number of calories you expend merely keeping the body functioning at rest.

    Consuming more calories than you expend is known as ‘Energy Surplus.’ This can be explained through the equation below:

    Energy Surplus = Energy taken in (Food + Drink) > (is greater than) Energy expended (exercise, metabolism, thermic effect of feeding)

    Action Plans for Underweight Issues are available in the website Club.

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    For more information on gaining weight, please visit the Weight gain page in the Weight section