Many individuals have difficulty maintaining their current weight or gaining weight. Being underweight – clinically defined as a BMI less than 18.5, but which can include a BMI above this level – can put an individual at risk for significant adverse health implications, including decreased immune function, low-density bones and teeth, fertility issues, hypothermia, and malnutrition. It also can have negative effects on exercise performance.

The key to achieving any health goal, in this case gaining weight, is to understand what is causing the problem and address the root cause. There can be many reasons for the inability to maintain or gain weight – and it’s often multifactorial.

1. Figure out why you can’t gain the weight you desire. 

Look to family members: Do they have a similar frame and body type? Did they have similar weight issues at your age? Genetics play a role, but just like athletic performance, intelligence, and other skill sets, weight manipulation almost always can be achieved by consistent, conscious effort.

Independent of the genetic component, here are several common underlying physiological reasons and how you can evaluate them:

  • Malabsorption in the gastrointestinal (GI) tract during digestion can be a cause. Foods and nutrients are broken down in the mouth and stomach and absorbed primarily in the small intestine. Symptoms that malabsorption might be a cause include changes in stool consistency, like color, shape, and regularity, or gas, bloating, and discomfort. Although it's a complex process, your microbiome plays a large role in maintaining the right environment for your gut cells to do their job. Thorne’s at-home Gut Health Test can help you understand your digestion capabilities and how you can influence your microbiome to optimize gut health for nutrient absorption.
  • Hyperthyroidism, or overactive thyroid, is when the thyroid overproduces the hormones responsible for regulating metabolism, resulting most notably in unexplained weight loss, among other symptoms. A quick finger-prick blood test using Thorne’s at-home Thyroid Test can help you understand if thyroid activity is influencing your weight. 
  • Acute stress episodes, mental or physical, can change hormones and chemical messengers, resulting in a loss of appetite and increased metabolism. Significantly recurring episodes can thwart your ability to gain weight. Recognizing stressful events and testing with Thorne’s Stress Test will help you understand if this is a problem for you.   
  • A change in your basal metabolic rate (BMR), where your body burns a significant number of calories at rest, might be an explanation. Typically as we age, BMR decreases for reasons like changes in muscle mass, brown fat, and mitochondrial capacity. Your BMR might be higher than you think. If you are unable to get the gold-standard indirect calorimetry analysis done, then easily accessible wearable sensors or portable metabolic devices can help you estimate your BMR to know how many daily calories you need.

2. Take a deep dive into your daily nutritional intake. 

Maintaining a sufficient intake of vitamins and minerals from both diet and supplements supports optimal metabolism. Some individuals have difficulty meeting their needs because they avoid specific food groups or are picky eaters, have a GI condition, or have higher needs like athletes or are still growing. In some instances, low body weight in a female can cause amenorrhea and impact bone density. Focusing on reaching daily micronutrient needs through diet and a multi-vitamin supplement should be a priority. B vitamins are especially important in metabolism. 

Record a week of food intake using an app that calculates total calorie intake and a breakdown of macronutrients – carbohydrates, protein, and fats. A food scale and measuring are the most accurate. 

The research1 on “the best diet to gain weight” shows it should be personalized, but there are ranges of macronutrients you can start with and tweak as you go. Weight gain, with a focus on increasing healthy, lean muscle mass, requires a daily caloric surplus (sometimes an extra 300-500 calories daily) and the right balance of macronutrients.

Calculate your daily calorie needs and aim to consume 20-30 percent of your calories from fat (mainly mono- and polyunsaturated fatty acids). Protein should be the main component of every meal and snack and should be 1.0-1.5 grams of protein per pound of current body weight daily. Ideally, the total gram amount will increase as body weight increases. The remaining daily calories should come from carbohydrates, with the best options being complex carbs like whole grains, starchy vegetables, beans, lentils, and other nutrient-packed options.

Avoid alcohol, empty-calorie foods like candy and desserts, and sugary soda drinks. These provide empty calories – not the type you want to build your physique with.

After you have formulated a diet plan, continue to track your intake to ensure you’re hitting your target of total calories and macronutrient percentiles.

3. Recognize how your movement and exercise routine (or lack thereof) might be hindering weight gain efforts.

Endurance athletes are aware of the effect that exercise duration has on their ability to gain weight. Although it seems counterintuitive, not exercising can be just as detrimental. Little movements, like fidgeting or an active standing job, can also subconsciously amount to a calorie deficit.2

Exercise plays an important role in putting on weight and muscle and will help you have an appetite throughout the day.3 Higher intensity exercises acutely decrease your appetite immediately following; whereas, low-to-moderate activity, like a leisurely swim or hike, tends to increase appetite. To focus on building muscle, you will want to lift heavy and strengthen big muscle groups like the back, shoulders, legs, and core. Almost all exercise helps move the bowels, potentially making room for your next meal. Because a sedentary lifestyle doesn’t allow muscles to break down or repair and rebuild, there is little chance you will put on lean muscle without proper movement.

Learn these pre-exercise and post-exercise fueling tips to provide the right types of nutrients, and add exercise and movement to your calorie tracker.

4. Be patient.

Just like weight loss, weight gain should be slow and steady, about 1-2 pounds weekly, to not overload or strain the body’s systems. And it should be noted that if you are seeking weight loss support, don’t do the opposite of what is recommended in this article. In fact, optimizing physiological function, formulating the right diet, and implementing exercises to reach your goal are all a part of a weight loss plan, too. 

References

  1. Leaf A, Antonio J. The effects of overfeeding on body composition: the role of macronutrient composition – a narrative review. Int J Exerc Sci 2017;10(8):1275-1296.
  2. Koepp GA, Moore GK, Levine JA. Chair-based fidgeting and energy expenditure. BMJ Open Sport Exerc Med 2016;2(1):e000152.
  3. Dorling J, Broom DR, Burns SF, et al. Acute and chronic effects of exercise on appetite, energy intake, and appetite-related hormones: the modulating effect of adiposity, sex, and habitual physical activity. Nutrients 2018;10(9). doi:10.3390/nu10091140