Fast food is incredibly convenient, and usually very tasty too, but it's not always the best option for refuelling our bodies. Over at comparison site, Fast Food Menu Price, there's a detailed infographic that shows the effect of eating one of the most iconic on-the-go meals of all time: the McDonald's Big Mac.

For the first 10 minutes, everything goes brilliantly, at least on the surface. Our brains have been wired to prefer high-calorie foods (sorry, dieters) and the Big Mac provides these calories in abundance - an average Big Mac contains 540 calories, which cause our blood sugar level to shoot up. Feel-good chemicals, like the neurotransmitter dopamine, are released into the brain, and you may catch yourself thinking: "This is a tasty burger."

It's from the 20-30 minute point that the downhill slide starts. The high levels of fructose corn syrup and sodium inside the bun leave us craving more of the same (and in the long term, this can lead to obesity, diabetes, and heart disease). Then the sodium - some 970 milligrams of it - causes dehydration and starts making the kidneys and heart work faster. Blood pressure rises, and you may well be tempted by a McFlurry or apple pie.

According to the infographic, at the 40 minute mark, the body will probably still be craving similar types of food: losing control of your blood sugar levels makes junk food (like a chocolate bar) seem even more appealing than it normally would. The gastrointestinal tract very quickly absorbs the high volume of fructose corn syrup we mentioned earlier, further adding to your hunger pangs.

From 50-60 minutes, the period of slow digestion starts in earnest. Food typically takes 24-72 hours to digest, but the grease and trans fat inside a Big Mac means the digestion time for the McDonald's signature burger can easily go beyond three days. "If you want to enjoy a Big Mac, try to keep it an occasional event," is the advice from Fast Food Menu Price. "The ingredients can cause serious harm to your body, especially when consuming them on a regular basis."

The infographic has been put together using data from McDonald's own website as well as articles from LiveStrong, Blood Pressure UK, and FoodMatters. McDonald's itself doesn't recommend living solely on a diet of Big Mac and fries - treat them as an occasional treat rather than a regular meal and you'll be fine (in fact, in small doses they can actually be good for you). At least now you know exactly what you're letting your body in for.

Fast Food Menu Price

Zoomable version here.