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What are the effects of calorie counting and intermittent fasting?

1) Dear Alice,

I've started counting calories in order to lose weight, and I've lost ten pounds in six months, so I'm positive that counting calories works. Recently I've started to eat one big meal (about 1400 calories) a day. Is this healthy? Will I continue to lose weight?

2) Dear Alice,

During the day, I keep a strict paleo diet and end eating at 10PM and Begin eating at 12 PM the next day. Around 10:30 AM the next day, I do full a body weight training session and begin eating at 12 PM. Basically, I only drink water during my fast or keep calories to a five calorie maximum. After the fast, I eat whatever I want (paleo that is). I'm trying to get my body to use excess fat as energy, therefore causing me to lose body fat and gain muscle faster. I feel great and I have witnessed fast results, (increased strength and leanness) within a month and half of intermittent fasting. My question is do you think intermittent fasting is unsafe? Or just a new an effective way to see increased health?

Dear Reader, 

The questions of calorie counting and intermittent fasting are complex and involve both physical factors and your personal goals for fitness and body composition. Whether or not either of these methods will continue to support your goals depends on many individual variables. Each person’s weight changes, muscle changes, and energy levels are personal, so what supports one person may not work as well for another. As you plan to make changes, speaking with a health care provider, registered dietitian, or personal trainer may be useful. They can assist you in making choices that help, rather than hinder, your goals. 

When it comes to losing weight, many people try a variety of methods and eating patterns including intermittent fasting (IF). With IF, eating times are spaced out. People might fast for 24 hours a few days a week or fast every other day. Others dedicate a specific time frame of the day (such as six, eight, or ten hours) to eating all their required calories and fasting for the remaining time. These cycles are shown to encourage the body to start using adipose tissue (fat) for energy rather than glucose (sugar or carbs). Some studies have also shown that intermittent fasting can help with weight loss and developing muscle mass. There may also be health benefits for people with heart issues or diabetes. 

Another common weight loss method is counting calories. Every person has different caloric needs based on their age, weight, height, activity level, and factors like medications or environment. This could mean that a middle-aged adult who has a sedentary lifestyle only needs about 1,600 calories per day, while an active young adult may need up to 3,000 calories or more per day. Decreasing the average number of calories that you eat in a day (caloric restriction) could lead to weight loss, while increasing it could lead to weight gain. However, it’s important to note that if calories are too low this could also lead to weight gain. This is because your body will lack the nutrients it needs, causing your metabolism to slow down. Losing weight slowly is likely to be more sustainable, with some experts recommending one pound per week. 

When thinking about both methods, there aren’t noteworthy differences when it comes to weight loss results as long as the person is still getting their essential nutrients and calories. However, studies on caloric restriction and IF are often conducted solely on people who are overweight. Therefore, even if you follow the exact same plan as someone else, how well it works for you in particular may vary depending on things like your genes and current body structure. Additionally, some people may find that caloric restriction or IF ultimately does more harm than helps. Some of these more vulnerable groups include children, the elderly, people who are pregnant, and those at risk of developing an eating disorder. 

Eating a variety of foods from all the food groups without restriction can help ensure that you're getting the appropriate vitamins and nutrients to support your individual caloric needs. Other eating plans may limit foods and it may cause you to miss out on nutrients in other food groups. It’s good to keep in mind that not eating certain foods may lead to nutritional deficiencies or side effects such as fatigue, exhaustion, or problems with body image and self-esteem. 

Every person has different food and activity needs. In order to help you figure out what may work best for you, some things to consider about both food and physical activity are: 

  • Flexibility: Are you eating foods from all major food groups? Are you restricting or limiting yourself from eating certain things? If so, why, and how might it affect you? What kinds of physical activities are you doing? How often do you exercise outside of that regimen? 
  • Balance: Are you eating enough to get your essential nutrients and calories? How much do you exercise each day or week, and does this factor in breaks or rest days? 
  • Enjoyment: If you’re looking for long-term change, is your current eating routine something that you find enjoyable? Will you be able to sustain it over time? What about your exercise routine? 

List adapted from Mayo Clinic 

Thinking about these different factors may help you decide if your current plans are helping you to meet your goals and are sustainable. After this reflection, you may still find it useful to meet with a health care provider, registered dietitian, or personal trainer to ensure you’re getting the most out of your food and movement.  

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Last updated Apr 19, 2024
Originally published May 26, 2006