Published 24th February 2022

How old are you when your metabolism begins to slow down?

If you feel like you’re putting on weight as you get older, or have less energy, you may be wondering whether your metabolism is slowing down. 

But at what age does this really happen? And what does it actually mean? There are two ways to think about metabolism. 

The speed that your body burns energy for its everyday functions is called your metabolic rate. For most people, this doesn’t start to slow down until around the age of 60, but it does change if your weight changes.

Your metabolic rate is different from your food metabolism, which is how your body digests and absorbs nutrients from what you eat. 

At ZOE, we run the largest nutritional research program in the world. It’s shown us that how you respond to the foods you eat is unique to you. 

Read on to find out more about metabolism, when it slows down, and what you can do to support your long-term metabolic health

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What is metabolism and why does it matter?

There’s a lot of confusion around the term metabolism — and for good reason.

What you may have in mind when you think about your personal metabolism is how fast your body burns calories. This is actually called your metabolic rate

Linked to this is your total daily energy expenditure, the amount of calories your body uses throughout the day. 

Metabolism itself is the name for the processes your body goes through to digest and absorb nutrients from the food you eat. When you metabolize food, it leads to rises in the levels of sugar or fat in your blood, followed by falls afterward.

Certain foods can make these rises bigger or last for longer. But as ZOE’s research has shown, how your body responds to different foods is personal to you.

This is important because prolonged or repeated big rises in blood sugar or fat levels can have a significant effect on your health, including your amount of body fat.

The ZOE at-home test analyzes your blood sugar and fat levels, and the bacteria that live in your gut, so you can find the best foods for you.

You can take a free quiz to find out more.

At what age does your metabolic rate slow down?

As we’ve seen, there are different ways of understanding metabolism. That means there are also different answers to the question, “what age does your metabolism slow down?”.

When it comes to metabolic rate — the speed at which your body burns calories — the answer may not be quite what you’re expecting.

A recent study looked at data from over 6,400 people aged between 8 days and 95 years old and found some very clear patterns.

According to the researchers, total daily energy expenditure goes through four distinct stages as people age. 

During the growth spurt from just after birth, the amount of energy you use increases rapidly, peaking at around 1 year. It’s about 50% higher than in adults when adjusted for body weight. 

It then gradually goes down again — by around 3% per year — but only until the age of 20.

What may come as a surprise is that your metabolic rate then levels out and doesn’t start to drop again until the age of 60, and then only by less than 1% per year.

The researchers didn’t find major differences in metabolic rate between men and women either when they adjusted for body size. 

However, these findings don't mean that the amount of energy you burn doesn’t change as you age. The researchers calculated the metabolic rate adjusted to the participants' fat-free mass. This term means their weight minus the fat in their body. 

So, in reality, if your body weight, or more specifically, your fat-free mass changes, then the amount of energy you burn each day also changes. 

For example, during pregnancy, the amount of fat-free mass changes dramatically due to the weight of the baby and the placenta. Your energy expenditure goes up in line with this. 

As you age, your body composition changes, and you tend to lose muscle mass, which makes up part of your fat-free mass. The older you get, the more muscle you lose, and the less energy you burn each day. 

You can slow down muscle loss as you age by doing exercise, particularly resistance training. 

At what age does your food metabolism slow down?

The way your body metabolizes food as you age is a different story, especially for women.

When you eat carbohydrate-rich foods, your blood sugar rises. Refined carbs, like sugar, white bread, and other highly refined grains can cause a steep increase followed by a big drop, to below normal levels. 

This is commonly known as a blood sugar “crash” and can cause tiredness, hunger, headaches, shakiness, and other symptoms.

Unprocessed carbs like those found in whole grains, beans, and vegetables don’t cause this crash. 

Similarly, when you eat meals with a lot of fat, especially saturated fat, your blood fat levels rise. However, fat takes much longer to clear from your blood than sugar, as much as 6–8 hours

Your blood fat levels don’t rise as much or stay up for as long with healthy, unsaturated fats like olive oil. 

If the levels of sugar and fat in your blood regularly remain high for a prolonged period, this can lead to a variety of short- and long-term negative health issues.

At ZOE, we use the term “dietary inflammation” to capture the unhealthy effects that can be triggered by the food we eat. 

Our research shows that earlier in life, women experience less severe blood sugar rises after eating than men. 

However, women’s post-meal blood sugar responses go up throughout adulthood, rising steadily into their 60s and beyond. 

While men’s blood sugar responses start out much higher than women’s, they remain relatively flat for most of their lives.

Data collected by ZOE scientists show that, on average, women experience larger post-meal blood sugar spikes as they get older.

But these changes are highly personal and depend in particular on how your body metabolizes specific foods.

Eating the right foods for your metabolism

ZOE runs the largest nutritional study of its kind, with over 15,000 participants so far. Our data has shown that, over time, the foods you eat can affect your blood pressure and cholesterol levels, as well as your weight. 

These factors are in turn linked to your risk of metabolic diseases like type 2 diabetes, heart disease, stroke, and kidney disease. 

Importantly, our research has also shown that everyone metabolizes foods differently, and that this can change with age. What’s more, your gut microbiome — the unique community of microorganisms that live in your gut — can influence this.

In short, there’s no one-size-fits-all approach to nutrition, so it’s crucial to understand how your body responds to particular foods.

Using the latest scientific techniques, the ZOE at-home test looks at your blood sugar and blood fat responses, as well as the makeup of your gut microbiome. 

Based on your individual results, you can find the best foods for your body, to reduce dietary inflammation and support your metabolic health. 

People who closely followed their personalized ZOE recommendations for 3 months lost weight — an average of 9.4 pounds — while over 80% said they had more energy. 

Take a free quiz to find out what the ZOE program can do for you.

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Summary

For many people, the term metabolism really means metabolic rate — the speed at which your body burns calories to keep its basic functions running.

Your metabolic rate does change during your early life, but it plateaus between the ages of 20 and 60, and only decreases by around 1% per year after that. Your total daily energy expenditure also depends on your weight. So, if your body composition changes, your energy expenditure will also change. 

Metabolism itself is the way your body processes food for energy and nutrients. It’s associated with responses such as increased blood sugar levels after eating. These also change with age, but they change very differently for men and women.

Men’s post-meal blood sugar levels stay relatively static as they get older, but women’s rise steadily through their adult lives.

These rises are important because they can lead to dietary inflammation. This can contribute to your risk of metabolic diseases like type 2 diabetes and heart disease, as well as increased body fat.

However, ZOE’s research has shown that everyone’s responses to food are different.

With the ZOE program, you can find the best foods for you at your current life stage. 

Sources

Daily energy expenditure through the human life course. Science. (2021). https://www.science.org/doi/10.1126/science.abe5017

Impact of the content of fatty acids of oral fat tolerance tests on postprandial triglyceridemia: Systematic review and meta-Analysis. Nutrients. (2016). https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5037564/

Low blood glucose (hypoglycemia). (2021). https://www.niddk.nih.gov/health-information/diabetes/overview/preventing-problems/low-blood-glucose-hypoglycemia 

Menopause and postprandial metabolic and inflammatory responses: a cross-sectional study exploring associations with sleep, physical activity and habitual diet. Proceedings of the Nutrition Society. (2022). https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/menopause-and-postprandial-metabolic-and-inflammatory-responses-a-crosssectional-study-exploring-associations-with-sleep-physical-activity-and-habitual-diet/0428F68D35B3F673E845AA9D6FFC72DB

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