Losing Weight by Eating More: A Look into the Human Metabolism
By Avance Care’s Registered Dietitian: Shannon Corlett, MS, RDN, LDN
It’s a strange concept that eating too little may be preventing you from losing weight, but a lot of people are surprised to see that a healthy meal plan for weight loss includes more food than they are currently consuming. Although you do need a calorie deficit to promote weight loss, for many people eating too little food can pose its own metabolic challenges. Achieving a healthy body weight is a complex process that involves not only the amount of food you eat, but also the type of food, your personal medical history, and trends in intake over time. When all of these factors are in line you have an increased likelihood of losing weight, but don’t be surprised if it takes more than just cutting calories to reach this goal.
Calories are a unit of measurement for energy- Just like you can measure your height in feet and inches, you can also measure your energy needs in number of calories. In order to determine how many calories you should be eating for weight loss, it is important to first understand how many calories your body actually needs in a day. Metabolism is the process by which your body converts your food and beverages into energy. Your basal metabolism (basal metabolic rate, BMR) defines how much energy your body needs at rest to maintain cellular activity, respiration, temperature regulation, and circulation. Basically, it’s the minimum amount of energy needed just to keep you alive for your current weight and body structure. This energy expenditure is considered your baseline, and then increases based on your food choices and activity throughout the day to get your total energy expenditure. The easiest way to determine your BMR is by using standardized equations that estimate your needs (i.e. the Mifflin-St. Jeor or the Harris-Benedict equation) or you can ask your Registered Dietitian to conduct a body composition test!
What Affects Metabolism and How Do You Improve It?
- Body composition– Muscle is a more metabolically active tissue than fat mass. Therefore, having more muscle mass allows you to burn more calories. Including strength training as part of your standard exercise routine helps to build muscle mass and will improve your overall energy expenditure.
- Sex– Men typically have more muscle mass than women, giving them increased resting energy expenditures. Both sexes can improve their energy output by increasing muscle mass.
- Age– Most people experience a gradual decrease in resting energy expenditure as they age due to a gradual decrease in muscle mass and a gradual increase in fat mass. However, this change is not biologically necessary, and maintaining a healthy diet and adequate physical activity as you age can counteract this effect.
- Size– Larger people require more energy and have a higher total energy expenditure. Calorie requirements may need to be adjusted as you lose weight.
- Hormones– Certain individuals have hormonal imbalances (e.g. hypothyroidism and Cushing’s disease) that affect weight and may require medical intervention.
- Diet and Calorie Intake– Consuming a balanced diet, with appropriate calorie intake, helps to maximize energy expenditure through food processing (thermogenesis).
How to Set and Achieve Healthy Weight Loss Goals
Once you know your daily energy needs, a healthy calorie intake for weight loss can be determined. For most people, weight loss of 1-2 pounds per week is a healthy rate to burn fat and preserve lean muscle mass. This is equivalent to a reduction of 500-1,000 calories per day below your energy needs. For example, a moderately active, premenopausal adult female needs an average 2,000 calories per day- To lose 1 pound per week, she would need to decrease her average daily intake to about 1,500 calories.
Low (and Very Low) Calorie Diets
As a Registered Dietitian, I often meet with individuals who have been “dieting” for months and months without any significant weight loss. It’s a terrible feeling, when you’re really trying to be successful and your weight simply will not budge. Many individuals who are seriously seeking weight loss will try a Very Low Calorie Diet (VLCD-less than 800 calories per day)… And initially it can work! For the first several weeks on a VLCD, metabolism is high and the body is forced to use energy stores to meet its needs. But this diet is not safe and requires medical supervision, with meals in the form of prepared formulas (shakes and bars) that ensure all nutrient needs are being met, to be successful over longer periods of time. Often, when attempted without medical supervision, weight loss on VLCDs completely stops after a short period of time. But there is hope, just a few weeks at an appropriate calorie intake can be enough to jumpstart weight loss.
Everyone has individualized calorie needs, but in general it is not recommended that women eat less than 1,200 calories and men less than 1,500 calories per day. These levels allow for weight loss without sacrificing vitamin and mineral intake as long as the diet contains mostly nutrient-dense foods. When the diet goes significantly below these levels over an extended period of time your body adapts to the low calorie intake. The proposed mechanism is that the metabolic rate of your cells changes with decreases in energy supply causing metabolic adaptations that reduce the total rate and amount of weight loss. Initially the low energy intake produces weight loss, but over time your cells become used to the change and actually use less energy to function. This leads to an overall decreased energy expenditure (decreased metabolism) and your body is able to function at the lower calorie intake without using stored energy (without burning fat mass). In addition to slowing or preventing weight loss, many people experience increased fatigue and lethargy when they are not consuming enough energy over time.
The Bottom Line
Metabolism and weight change is a complex process that is affected by everything from body composition and calorie intake to genetics and stress, but there are many steps you can take to promote healthy weight loss. Maintaining structured physical activity that includes both cardiovascular exercise to burn calories and strength training to build muscle mass helps increase basal energy expenditure and total energy expenditure throughout the day. Eating a healthy, balanced diet that includes a sufficient calorie deficit without severely restricting intake promotes maximum expenditure for energy conversion at the cellular level. Making small changes to energy intake and expenditure is often enough to defeat a weight plateau. And, most importantly, remember that weight loss is an individualized process where the same approach does not work for everyone. Achieving a healthy weight can be a challenging process, but it’s worth it when you stay committed to your goals and celebrate small successes along the way.
Learn More About Caloric Needs and the Healthy Way to Lose Weight: Avance Care Nutrition Services
Heymsfield SB, Harp JB, Reitman ML, Beetsch JW, Schoeller DA, Erondu N, Pietrobelli A 2007. Why do obese patients not lose more weight when treated with low-calorie diets? A mechanistic perspective. Am. J. Clin. Nutr. 85, 346–354.