While people sometimes think of cardio as a good way to lose weight, this isn't necessarily always the case. Sometimes people stay at the same weight or even gain weight despite doing regular cardio workouts. This could be due to a number of reasons, including overestimating how much cardio you're doing, underestimating how many calories you're eating or even a medical condition or a medication you're taking.
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Overestimating Calorie Needs
Diet usually has more of an effect on weight than exercising, so if you're gaining weight, you could be overestimating how many calories you need. Men typically need between 14 and 18 calories per pound of body weight to maintain their weight, depending on their activity level, and women usually need between 12 and 16 calories per pound of body weight. People sometimes overestimate how many calories they burn through their daily workouts and activities and think that they need more calories than they really do. This can cause them to eat too much and gain weight. A study published in the Journal of Sports Medicine and Physical Fitness in December 2010 found that people tend to estimate that they burned three to four times the number of calories than they actually burned during their exercise sessions, and then when asked to eat just enough to compensate for the calories they burned, they consumed more than twice as many calories as they'd burned.
Gaining Weight From Eating Too Much
People often overcompensate for the number of calories they burn through exercise by eating more, and this limits weight loss resulting from the exercise, notes a study published in Obesity Reviews in 2012. It's also easy to underestimate how much you're eating. People sometimes forget to factor in the calories from beverages, condiments and instances when they had a taste or two of a food instead of an entire serving. A study published in the British Medical Journal in 2013 noted that people tend to underestimate how many calories they've consumed at fast-food restaurants, especially if they have a larger meal.
To lose weight at a rate of 1 pound per week, you need to create a calorie deficit of about 500 calories per day either by eating less or exercising more. Don't cut calories too much, however. Getting too few calories per day can slow down your metabolism and increase your risk for weight gain. Men should get at least 1,800 calories per day, and women need at least 1,200 per day to minimize any adverse effects on metabolism.
Ineffective Cardio Exercise Methods
You may be doing a lot of cardio, but if it isn't at a very high intensity level and if you don't do resistance training as well, it may not lead to weight loss. For example, for a 160-pound person, walking at a speed of 2 miles per hour only burns about 204 calories per hour. Having an extra snack could easily counteract any benefits from this cardio. An hour of resistance training would burn about 365 calories for a person this size, as well as helping build muscle. Adding muscle increases your metabolism, as muscle takes more calories to maintain than fat. Without resistance training, about one-fourth of any weight you lose will come from muscle instead of fat, so it's important not to skip this type of exercise. Of course, if you eat too many calories, your exercise may lead you to gain muscle without losing weight, and this could also explain your weight gain.
Resistance to Exercise-Induced Weight Loss
In general, the more cardio you do and the more vigorously you exercise, the more weight and body fat you'll lose, according to a study published in the Archives of Internal Medicine in 2004. Some people, however, tend not to lose as much weight as expected through exercising. People often compensate for the amount of exercise they do by either reducing their other activities or eating more calories, thus minimizing the potential for weight loss. A study published in the Journal of Strength and Conditioning Research in 2015 noted that if a person doesn't experience changes in weight and body fat after four weeks of exercise, he may be a compensator, and cardio may not be as effective for weight loss for him.
Potential Medical Issues
Check with your doctor to see if there's a medical reason for your unexplained weight gain. Taking certain medications, including diabetes medications, those used for treating mental health issues, birth control pills or corticosteroids, could increase your risk for weight gain. Having an underactive thyroid, going through menopause or suffering from polycystic ovary syndrome or Cushing syndrome could also make you more likely to gain weight.