A Functional Medicine Approach to "Slow Metabolism": Middle Age

by 
Dr. Eve Henry, MD
A Functional Medicine Approach to "Slow Metabolism": Middle Age

Middle-age weight gain seems to be an unavoidable rite of passage for most Americans. On average, middle-aged adults gain roughly 1.5lbs a year. Doctors have assumed for decades that the common weight gain seen in middle age was caused by a general “slowing” of the metabolism that occurs as someone moves through the fifth and sixth decades of life.

However, a recent study in Science has laid that theory to rest, proving metabolic rates of energy expenditure are very stable from ages 20 to 60.

So why do we gain weight in our 40s and 50s? For better or worse, the answer is complicated. There are many possible health problems that become more common as we age and, when left untreated, will drive a slow and steady weight gain.

This article will discuss two of the most common causes of middle-age weight gain: muscle loss and reductions in sex hormones.

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Signs & Symptoms of Middle Age Slowed Metabolism

Men and women in their 40s and 50s often complain that they continue to gain weight no matter what they do. Individuals who have adhered to a regular exercise regimen and a healthy diet for decades suddenly can’t stop the scale from inching upwards. They also notice that the weight tends to cluster around their abdomen. These excess pounds seem to bend the laws of physics and refuse to budge despite increases in exercise, changes in diet, and all of the old tricks that worked so well for the same individual ten years prior.

Possible Causes of Middle Age Weight Gain

Muscle Loss Increasing Insulin Sensitivity

Muscle mass decreases roughly 3-8% per decade after age 30. This physiologic loss is compounded by the lifestyle changes that bring most of us to spend our days sitting at a desk by the age of 40.

This loss of muscle mass has profound and immediate impacts on insulin sensitivity. Muscle tissue is a key destination for glucose. The decrease in muscle mass and increase in fat tissue that occurs as we age is thought to be a key driver in the rise of age-associated insulin resistance.

When insulin is released, muscle tissue removes glucose from the bloodstream, lowering our blood glucose levels. The less muscle tissue present, the less help we receive removing glucose from the bloodstream in response to insulin release. Higher glucose levels lead to higher insulin levels and push our physiology down the path of insulin resistance. Elevated levels of endogenous insulin have profound metabolic effects that lead directly to weight gain.

Functional Medicine Labs for Muscle Loss and Insulin Sensitivity

Fasting insulin, HOMA-IR, Hgba1c

It is imperative that we detect signs of insulin resistance as early as possible. Fasting insulin is one of the first detectable changes in the path to insulin resistance. You can use fasting insulin to calculate the HOMA-IR, which is a composite score that helps stratify a patient’s insulin resistance. HgbA1c gives you a proxy of someone’s three-month average blood glucose levels. Taken together, these three tests can help identify patients who are developing insulin resistance.

Body composition analysis

While BMI measurements and simple scale weight can provide clues to someone’s body composition, it is very difficult to discern fat vs. muscle using these metrics. A DEXA scan can offer a clearer picture of muscle mass vs. visceral adiposity. Using a DEXA scan also allows you to track an individual’s muscle mass with time and intervene if their muscle mass begins to decline.

Functional Medicine Treatment for Muscle Loss and Insulin Sensitivity

A comprehensive approach to weight loss in an aging individual should include strength training. Even a single exercise session has been shown to positively influence glucose uptake by muscle.

The effect of strength training and exercise can have long-lasting effects on glucose regulation, with one study showing an increase in glucose uptake 16 hours after a single exercise session.

Although prescriptions vary based upon individual needs, 20 to 30 minutes of strength training three times a week can go a long way to reversing age-related muscle loss.

Possible Causes of Middle Age Weight Gain

Declining Sex Hormones

Although estimates vary, the average woman gains between 5-8 lbs pounds during the menopause transition. A large observational study followed women in their 40s and 50s for six years and found the average weight gain to be roughly 7.5lbs with an associated 5.7 cm increase in waist circumference. The change in waist circumference was positively correlated with a rising FSH (a key hormonal marker of menopause).

Although the exact mechanism of why declining hormone levels cause weight gain is unknown, studies have shown that the hormonal changes associated with perimenopause and menopause were associated with an increase in ghrelin, the hunger hormone.

Lower estrogen levels were also shown to impair the function of leptin and neuropeptide Y, hormones that help our body regulate appetite and control the sensation of fullness. These findings suggest that decreases in sex hormones may cause a significant dysregulation in our appetites and physiologic responses to food.

The negative effects of declining sex hormones in middle age are not limited to women. Men experiencing a decline in testosterone levels are significantly more likely to be obese than their peers with normal testosterone levels.

The relationship between excess fat and testosterone is bidirectional, with excess adiposity suppressing the production of testosterone. Declines in testosterone and the associated weight gain can induce a self-perpetuating cycle of metabolic dysregulation in middle-aged men.

Functional Medicine Labs for Declining Sex Hormones

Rupa offers multiple methods for assessing male and female hormone levels in blood and saliva. ZRT, Boston Heart, Genova, and Vibrant Health Labs all offer progesterone, estradiol, FSH, and testosterone assessments that will help inform whether or not declining hormone levels are a root cause problem for your patient.

Functional Medicine Treatment for Declining Sex Hormones

Hormone replacement therapy in the appropriate individual may prevent some of the harmful metabolic consequences associated with middle-age.

One study found that estrogen replacement therapy altered the fat distribution in menopausal women preventing the high-risk central adiposity pattern.

In obese men with low testosterone, testosterone replacement has been shown to produce sustained weight loss. A study for over 400 men with low testosterone who replaced testosterone levels noted an average weight loss of between 37-66 lbs with more significant weight loss in individuals who were more obese at the start of the study.

Summary

Middle-aged weight gain is not a foregone conclusion. There are numerous physiologic processes that occur in middle age and increase our susceptibility to slow and steady weight gain.

Two common root cause issues are a loss of muscle mass and declining sex hormones. With careful analysis and early diagnosis, we can correct these imbalances and prevent middle-aged weight gain.

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References

Dr. Eve Henry, MD
Website
Dr. Eve Henry is board certified in Internal Medicine and Integrative Medicine. She is a concierge internist with a focus on optimizing healthspan and personalized wellness. 
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