The activity level categories are defined as follows:

• Sedentary: Typical daily living activities such as household tasks, walking to the bus, light activities while sitting, driving, shopping.
• Low Active: Typical daily living activities plus 30 to 60 minutes of moderate activities such as walking or cycling leisurely, golfing without a cart etc.
• Active: Typical daily living activities plus at least 60 minutes of daily moderate activity. cycling (leisurely), golf (without cart), swimming (slow), walking 3-4mph, etc.
• Very Active: Typical daily living activities plus at least 60 minutes of daily moderate activity plus an additional 60 minutes of vigorous activity or 120 minutes of moderate activity

Based on the body parameters shown, the results are the predicted for the different levels of physical activities. Energy intakes above the level would be expected to result in weight gain, whereas intakes below that level would be expected to lead to weight loss.

Eating Too Few Calories

Women should not eat less than 1,200 calories a day, and men not less than 1,500 calories a day. Nutrition therapists will tell you that food group targets and nutrient recommendations will not be met below those levels. Consult a doctor for guidance and support if you are considering a diet of less than 1,000 calories per day. By eating too few calories, you are at increased risk of the following:

Slower Metabolism

Eating too few calories may make weight loss slower and more difficult by slowing your metabolism. Your body may sense that food is in short supply and will slow down your metabolic rate to try and protect it from starvation. It can occur even if you are overweight and deliberately trying to lose weight. The slower the metabolic rate, the slower the calorie burn. Different people respond differently to low-caloric restricted diets. For some, their metabolic rate is slightly reduced, while for others, it is far greater. This variability accounts for the variability in weight loss rates between people. A lowered metabolism may continue long, even after going off the diet. It can also cause muscle loss, further decreasing metabolism.

Fatigue

Consuming too few calories can make meeting your daily nutrition needs more challenging. The diet's lack of essential nutrients ( protein, vitamins, and minerals) can lead to fatigue and health problems.

Hair Loss

Riboflavin, biotin, folate, and vitamin B12 deficiencies have been associated with hair loss. If your body doesn't receive enough of these nutrients, it can lead to hair loss. Also, sudden changes in weight due to dieting can cause temporary hair loss called telogen effluvium.

Reduced Fertility

Women severely restricting their calorie intake can experience disruptions in their menstrual cycles, making it more difficult to conceive. In men, it can reduce sperm count and motility and lower testosterone levels, reducing fertility.

Weakened Bones

Your body may reduce the production of certain hormones, including estrogen and testosterone, essential to bone health. Also, calorie-reduced diets are usually lower in calcium and other bone-healthy nutrients, which can decrease bone mass.

Lowered Immunity

A balanced and healthy diet is essential for a functioning immune system. When you don't consume enough calories, your body may not get the nutrients it needs to support immune function, leading to decreased infection resistance and longer recovery times from illnesses.

Insomnia

A lack of some nutrients, such as magnesium, due to consuming too few calories can also contribute to sleep problems. Magnesium is essential in many bodily functions, including regulating sleep. It helps regulate melatonin production, a hormone that promotes healthy sleep-wake cycles. Magnesium also helps regulate the neurotransmitters responsible for calming the brain and reducing anxiety, leading to better quality sleep.

Constipation

You may not get enough fiber when you consume little food, which is crucial for maintaining regular bowel movements. Also, when you eat less than the amount your body needs to function correctly, the body conserves energy by slowing the digestive process and reducing bowel movements, which can cause constipation.

Feeling Cold all the Time

A slowed metabolism can decrease your core body temperature, making you feel cold. Your body may also divert blood from your extremities and towards your vital organs, making you feel cold, particularly in your hands and feet.

An Ideal Body Weight

Your body fat percentage may be a better indicator of health than body weight alone. An ideal weight would be one that puts you in a healthy body fat percentage category. You can use the Body Fat Calculator found on this site to calculate what percentage of your body is fat and find a target weight that would correspond to a healthy percentage of body fat for you.

Your Body Shape is Important Too

Numerous studies have found that having an apple shaped body or carrying excess belly fat is riskier than having a pear shaped body or heavy bottom. Even normal-weight people with excess belly fat have an increased risk of health problems. You can use the Body Shape Index calculator found on this site to assess your mortality risk related to your body shape.