Changes in metabolism that causes weight gain as we age
In my last blog (why calorie restricted diets make you fat), I explained about the power of the hormone insulin to shunt surplus energy (glucose from food) into fat cells.
If we eat high sugar foods with a high glycemic index (GI) it causes a spike in insulin levels and a rapid storing of the surplus as fat.
With that background we can now come to the main topic of this series of blogs: – the changes in metabolism that causes weight gain as we age. Because we all know how easy it seems that young people can burn off excess energy.
In fact I remember very well how I was quite lean all the way through my 30’s and even into my 40’s, and then suddenly that dreaded middle-aged-spread started, and it has become harder and harder to halt the weight gain. So this blog is relevant to both men and women.
We all know that as we age our bodies change. It starts with a slow and gradual reduction in sex hormones (estrogen in women and testosterone in men) from as early as 30 years. This leads to a reduced basal metabolic rate (BMR). Using the analogy of our body as a car motor, the BMR is the rate the motor idles at.
When we are younger we are more ‘high rev’. As we age we slow down and ‘idle’ slower. The higher we rev, the more energy we burn just sitting still. As we age we end up burning less energy.
We also start to lose muscle mass as we age. And our muscle mass is the engine that burns the energy (fuel) that we eat (calories in food). So if we eat the same amount of food but burn less, then the surplus energy goes into fat storage.
This energy metabolism is happening in every cell in our body and is controlled by our genes. Our genes dictate what enzymes our cells produce, whether we make fat burning enzymes or fat storing enzymes.
New research in the field of epigenetics has discovered that our genes can be switched on and off by our lifestyle such as what we eat (specific nutrients), what we are exposed to and even what activities we do, including what we think about!
Yes, that is right. We can literally turn certain genes on or off by our behaviours.
This is very well described in the book The Fat Switch by Richard J. Johnson M.D.
So, as we age we have:
- Decreased sex hormones
- Decreased basal metabolic rate
- Decreased muscle mass
- Reduced energy expenditure
- More fat storing enzymes
- Less fat releasing enzymes
This all leads to an energy surplus. This surplus is stored as fat in fat cells.
As we get fatter we have even less energy. It is harder to exercise, so we do less, which means our muscles shrink more, our BMR declines more and it becomes a vicious cycle. The fat switch has been turned on and the weight gain we observe in our middle years begins.
But if you are a menopausal woman, and your estrogen levels are declining, your fat cells are trying to expand anyway, to produce estrogen (refer to Leigh Kite’s blog “menopausal weight gain” which explains why this is so).
So now you have surplus blood glucose, hungry fat cells, more fat storing enzymes, less fat releasing enzymes, less muscle to burn it, and reduced metabolism – BOOM – the fat switch is turned on! You now have the perfect storm for fat building and piling on the weight.
(The arrows in this diagram illustrate the enzymes that store and release fat. They do not reflect the exact number of enzymes; they are to help you visualise how female fat cells function. Menopause Without Weight Gain by Debra Waterhouse.)
What can you do about it?
Whether you are a man or a woman, avoid energy spikes and especially avoid insulin spikes caused by high GI meals. Here are some tips on how to do this:
- Avoid calorie restricting diets. Aim for healthy eating instead.
- Eat smaller meals more regularly – five or six smaller meals through the day is best. One or two of these could be a satisfying protein shake, which provides satiety in a convenient way. This helps reduce hunger and cravings and you are less likely to over-eat.
- Minimise intake of sugars (sweets, desserts etc), high GI foods, processed packaged foods (they often have hidden sugars), and alcohol, especially beer.
- Exercise regularly, but not fanatically (see our earlier blogs). There will be more on this topic in future blogs.
- Drink plenty of water.