We’ve all heard it before: “Exercise is important! Get your 30 minutes for 5 days a week in!” as if it’s a perpetual ad cycling through our phonological loop non-stop. This is yet another source of propaganda to support a healthy lifestyle, but this one will explain just how critical physical activity is!
When muscles contract, as they do a lot during exercise, myokines (proteins that signal the body, secreted from muscles specifically) and other signaling proteins are released. They go on to affect the entire body, as receptors for these proteins are found on pretty much all types of cells (muscle, fat, liver, pancreas, bone, heart, immune, brain). So exercise really does have an impact on the entire body. –groan– Here’s the gist that you’ve heard before but with fancier terms: physical inactivity leads to abdominal adiposity (blubber around your belly), which leads to macrophage infiltration of visceral fat (macrophages invade tissues), which leads to a chronic systemic inflammatory response (from macrophages secreting TNFa), which leads to things like insulin resistance, neurodegeneration, and tumor growth.
Let’s look at what all of this actually means. Macrophages are white blood cells (part of the immune system) that are formed in response to an infection or accumulating damaged or dead cells — they recognize, engulf, and destroy target cells. Tumor necrosis factor alpha, or TNFa, is a marker for inflammatory and immune responses; when it is secreted (by the macrophages), it causes damage to arteries and increases insulin resistance in muscles. Another player in this is Interleukin-6, or IL-6, a myokine released during contractions during exercise (up to 100x more than baseline) from muscle fibers. It acts both locally within the muscle and like a hormone in circulation. This magical molecule is a TNFa inhibitor, calming down the inflammation response. Brain derived neurotrophic factor, or BDNF, has strong effects on peripheral metabolism, which influences fat oxidation and the size of adipose tissue. Skeletal muscle BDNF is a key modulator in metabolic diseases and may be expressed as a compensatory neurotrophic factor against diabetic neuropathy or myopathy. This beautiful thing is upregulated with exercise!
“Yeah, whatever, what’s the worst that could happen?” –cue Beethoven’s Symphony №5– Well, aside from death, you can experience a myriad of excruciating side effects because of the lack of exercise. You could have a stroke (a brain region isn’t irrigated anymore because a clot blocked the blood flow). This can be moderated by exercising before the stroke, resulting in an increase in TNFa levels, which downregulates its receptors, which decreases infarct (a small localized area of dead tissue resulting from failure of blood supply) volume. However, if you work out too soon after the stroke, the levels of pro-inflammatory cytokines and cell stress markers increase (eventually they do decrease). Another potential vice: the combination of C-reactive protein (marker of inflammation level), impaired glucose control, and high blood pressure induces cognitive decline. Exercise has been shown to help Alzheimer’s and depression. So yes, it is better to just pump out a little sweat and keep those macrophages chilling.
“So where’s the proof?” One study looked at how men who walked about 10,000 steps a day physically reacted to only walking 1,500 steps a day: they experienced impaired glucose tolerance, a decrease in postprandial (after a meal) lipid metabolism, a 7% increase in intra-abdominal fat-mass, a decline in peripheral insulin, a 7% decrease in VO2 Max (a marker for cardiovascular fitness), and a decline in leg muscle. Another study proved that it isn’t necessarily the shedding of pounds that signifies an improvement in physical state: participants underwent intense exercise regimens for 12–16 weeks to combat abdominal obesity. The results showed a reduction in total fat, abdominal fat, and waist circumference, while there was an increase in skeletal muscle mass. Their weight didn’t change, as it was compensated with extra food. A study that looked at pregnant mice on high fat diets saw that lower exercise led to a lower proportion of phosphorylated Protein Kinase B (important for glucose metabolism, apoptosis, cell proliferation, transcription, and cell migration) in adipose tissue, more likely insulin insensitivity, and decrease glucose tolerance. It was also found that mothers who were fed a high fat diet but exercised (the best outcomes were seen if they exercised before and during pregnancy, as they had neural progenitor cells that branched more and extended further) had significantly better outcomes than those that didn’t exercise. The latter group was speculated to have also doomed their offspring to not be able to get many positive benefits from exercise.
But wait — not all hope is lost! Eating certain things will mediate your cognitive function from exercise: almonds, lettuce, dark chocolate, (green) tea, skins of foods, and berries with deep red color. All of these have flavanols, which promote healthy blood vessel function. So after you’ve completed your soon-to-be-newly-established workout regimen for the day, go and enjoy a nice cup of chocolate milk (double bonus with the calcium) and brace yourself for the opened doors of improved cognitive performance.