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Part 1: Why Is It Harder to Lose Weight as You Age?

Do you feel like after your 20s, you seem to put on weight more easily and losing it takes a lot more work than it used to? Worse yet, is age-related weight gain.


In this article, Part 1, we’ll explain why. In the next article, Part 2, we’ll explain our framework that can help you lose weight and look great at any age. 

Does Your Metabolism Slow Down With Age?

The short answer is no, between the age of 20 – 60. However, there are caveats and nuances because accurately measuring human metabolism is challenging.

In a 2021 study published in Science, researchers used doubly-labeled water to measure the metabolism of diverse 6421 subjects aged 8 days to 95 years. They found that our energy expenditure changes throughout 4 stages of life, including:

  1. Neonates: from birth to 1 year old. Babies were born with similar energy expenditures as adults, but this increased rapidly to about 50% more than adults per unit of body weight. Their rapid growth contributes to this large energy expenditure.
  2. Juveniles: from 1 to 20 years. Total and basal energy expenditure increases with age along with fat-free mass, although size-adjusted energy expenditure goes down until 25 years of age.
  3. Adulthood: from 20 – 60 years. Now is when basal and total energy expenditure and fat-free mass remain stable.
  4. Older adults: >60 years is when total and basal energy expenditure decline, along with fat-free mass and fat mass.
blond woman looking at the camera

Given the surprising findings, you might be wondering what could be happening if it’s really not your metabolism and you’re not 60 yet. This study also does not explain the 0.5 – 1 kg (1 – 2.5 lbs) that an average adult gains every year

Like any other nutrition study, there are nuances and caveats:

  1. The authors find that total energy expenditure correlates with fat-free mass up until around the age of 40. Although this study found the muscle and fat mass to be quite stable throughout the adulthood phase, it’s universally accepted that age-related muscle losses start in the 30s.
  1. Physical activity (green line) based on accelerometer declines with age. Tissue metabolism (black line), such as those calories burned in the brain and liver follows.
  1. Eating a caloric surplus is very common, especially in the US where portion sizes are extremely large. Could it be that the negative health effects of overeating get larger as you get older well before the age of 60?

Alexis Welker, a professor of biochemistry, physiology, and applied nutrition argues in his Letter to the Editors that many adults do in fact experience a major drop in their metabolism. This is especially the case if they’ve attempted to diet and lost some weight. 

However, the statistical models in this study may not accurately explain this phenomenon in so many adults. He also disagrees with the study’s statement that human metabolism is stable even during pregnancy. Therefore, the results of this study should be taken with a grain of salt. 

Doubly-labeled water measurements aside, let’s dive deeper into why it feels like your metabolism is slowing down and what you can do about it. 

Why Does It Feel Like Weight Loss Is So Much Harder as You Get Older?

Before we get into the nitty-gritty, know that weight loss is feasible at any age if you can create a caloric deficit. But, several factors can make it more difficult as we get older. There are also genetic components to metabolism and body weight, which can become clearer as we age.

Let’s unpack some factors that might be impacting your ability to lose weight, and what you can do about it.

elder woman working in the garden

1) Nutrient Status Due to Declining Gut Function/Absorption of Nutrients

When we think about weight gain, we often worry about how many calories we consume. This makes sense – if we eat less, we should lose weight. And while that’s true, many micronutrients help your cells burn calories for energy, while amino acids help you maintain or build muscles. 

Therefore, age-related decline in digestion and nutritional sufficiency can lower your metabolism, resulting in a subtle reduction in energy and brain functions.

In fact, older adults are at the highest risk of having a nutritional deficiency. They are also at the highest risk of being malnourished. As people age, changes occur in the digestive tract, starting as early as age 40. The decrease in nutrients and changes in gut function make it hard to manage weight. This affects control over food intake, gut health, digestion, and absorption.

Here is why:

–   Reduced efficiency: The production of digestive enzymes can decline with age. Enzymes break down carbs, proteins, and fats into smaller parts that can be absorbed. If you have fewer digestive enzymes, digestion becomes less efficient. This can cause problems with absorbing nutrients and lead to deficiencies.

–   Low stomach acid: Aging is often associated with a decrease in stomach acid production. Your stomach acid is important for breaking down food, especially proteins. It also helps your body absorb specific nutrients like vitamin B12, iron, and calcium. So when stomach acid is low, you run the risk of becoming deficient in these nutrients.

–   Microbiome changes: We see changes in the composition of our gut microbiome as we age. These organisms in our digestive tract are important. They help us digest food, absorb nutrients, and make vitamins. The efficiency of these processes could be affected by changes in this environment. It could also cause inflammation in the gut and digestive problems.

–   Digestive disorders: As we get older, we have a higher chance of developing digestive disorders. These disorders can affect how our bodies absorb nutrients and disrupt the usual digestive processes.

–   Dehydration: Older adults can be at a higher risk for dehydration. This can impact digestive processes and nutrient absorption. Hydration is also important for gut microbiota to function properly.

All these factors can impact your nutrient status and contribute to challenges with weight management. This is because nutrients are important for an efficient metabolism and proper management of appetite and cravings. Optimizing your micronutrient status might play a key role in helping you achieve your ideal body weight.

asian woman in the forest

2) Stress and Cortisol

Stress can trigger the release of a hormone called cortisol. Cortisol plays a big role in your body’s fight-or-flight response. As we age, we tend to see a noticeable increase in the average daily cortisol level. Having too much of it can contribute to poor blood sugar control, increased appetite, emotional eating, and belly fat.

3) Age-Related Decline in Muscle Mass

Even if you stay active in older age, research shows that there is a decline in muscle mass every decade of life – beginning in your thirties. And if you don’t stay active, things can become even worse.

Over time, a loss of muscle mass can morph into a condition known as sarcopenia. Sarcopenia often happens with more fat and less muscle, which lowers metabolism because muscles burn more calories.

Less muscle mass can impact how easily you’re able to lose weight in a few ways:

–   Lower resting metabolic rate: Muscle tissue is a highly metabolic tissue – it burns calories even when you are resting. As muscle mass decreases, your body’s metabolic rate also decreases. This can make it easier for you to put on weight and harder to get it off.

–   Changes in glucose metabolism: muscle tissue plays an important role in how your body metabolizes sugars. Less muscle can impact your insulin sensitivity, which can lead to insulin resistance. This can make it more difficult for your body to regulate blood sugar levels, and impact weight.

–   Less exercise tolerance: when you lose muscle, your strength and endurance can suffer. When you don’t feel strong enough to exercise, physical activity becomes more challenging. This can lead to increased sedentary behaviors, creating a vicious cycle.

More physical discomfort. Muscles help stabilize joints and regulate inflammation [R15]. When you have more physical discomfort, you’re less likely to move around, burning fewer calories overall.

Combined, all these factors can make it more difficult to lose weight.

4) Less Restorative Sleep

If you don’t sleep well, it’s going to be very hard to achieve or maintain your weight loss. As we get older, sleep quality can decline. It may take you longer to fall asleep, you may wake up more often during the night, or even spend more time napping. All of these changes can impact your overall health, and your ability to lose weight.

As people age, there are changes in normal sleep architecture. We get less of that deep, restorative sleep. Instead, we tend to spend more time in lighter sleep stages. These changes can impact hunger hormones and consequently, appetite control.

Lack of sleep or poor quality sleep can also cause hormone problems. Lack of sleep can make you feel more hungry by increasing ghrelin, the appetite hormone. At the same time, it may also reduce leptin, the hormone that makes you feel full.

Aging is also linked to shifts in circadian rhythms, affecting the timing of sleep and wake cycles. These disruptions can affect how your body processes food and how it responds to insulin, which can lead to weight gain.

Finally, poor sleep can reduce energy and motivation, making it more challenging to hit the gym or get out for a walk. And as we already learned, physical inactivity is a risk factor for weight gain and metabolic issues.

young woman getting up from bed

5)  Life Events Like Parenting, Caretaking, and Jobs

When life gets busy, health can be pushed to the wayside. As people get older, they have more things to do and this can affect their health and weight. Juggling these many responsibilities can leave you with limited time to focus on health habits, like exercise, sleep, and a healthy diet.

Parenting often requires putting your children’s health above your own, which can cause you to neglect your health. One big way this can lead to negative health impacts is in the realm of sleep. Mothers often report poor sleep quality. These sleep disruptions can lead to less physical activity, lower intake of healthy foods, and more emotional eating.

Work-related factors can also have impacts. Jobs that require long hours of sitting or minimal physical activity can lead to a more sedentary lifestyle. This can have negative impacts on weight. 

In fact, some researchers found that those who were active in the workforce tended to have higher body weights compared to those who were not, and these impacts were stronger in women. Job stress can also impact sleep, weight, and even lead to other issues like emotional eating.

Caretaking for a family member or loved one can be both emotionally and physically demanding, causing burnout and stress. Caretakers don’t have much time for taking care of themselves, like exercising or planning meals.

6) Menopause and Andropause

Menopause and andropause, the hormonal changes in women and men as they age, can have significant impacts on weight management.

Menopause involves a gradual decline in estrogen, which can lead to more belly fat. During andropause, men may experience a gradual decrease in testosterone, which can lead to weight gain. This weight gain is often concentrated around the midsection. These hormonal shifts influence the function of mitochondria, the powerhouse of our cells.

Mitochondria play a crucial role in energy production and metabolism. Changes in sex hormones can affect how mitochondria use fuel, such as altering glucose response to food. This can affect how the body uses and stores energy, which can cause weight problems. 

During these life stages, it’s crucial to adopt a healthy lifestyle with a healthy diet and exercise. You may even wish to work with a nutritionist to track your blood sugar response to food. This helps support overall well-being and effective weight management. 

african-american woman running

7) Age-Related Inflammation (Inflammaging)

As you age, your background chronic inflammation goes up. Researchers are still discovering more about this phenomenon called inflammaging, but contributors include:

  • A longer history of exposure to pathogens just because you’ve lived longer
  • More leaky gut resulting in higher blood lipopolysaccharides
  • Reduced autophagy
  • Hormonal changes
  • Reduced cellular antioxidant capacity
  • Obesity, especially in visceral fat (which is also worsened by inflammation)

This age-related inflammation can contribute to brain signals that increase appetite, reduce calorie expenditure, and hamper blood sugar control. At the same time, it can also reduce movement and increase the destruction of fat-free tissues such as muscles and bones. 

In a clinical study, inflammation levels based on IL-6 correlated with psychomotor slowing and body mass index.


Although a direct measurement showed that the human metabolism is stable between the ages of 20 and 60, most Americans steadily gain weight every year. Age-related weight gain is real, with many contributing factors such as declining gut health, stress, lower sleep quality, hormones, and inflammation.

In the next article, Part 2, we’ll cover what you can do to mitigate age-related decline in metabolism so you can lose weight and look great at any age.

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