If I eat really crappy food, like McDonald’s, before work where I walk upwards of 6 miles a day or more, I’m obviously burning off some of the bad stuff in the food, but why? What makes walking burn off and lower the consequences of eating really bad food?
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It doesn’t burn off the “bad” stuff. It burns off the calories. The bad stuff would be considered inflammatory like vegetable oils, deep fried, nasty additives etc. so you are not negating the negative aspects of trash food you are just compensating for the additional calories because you are active
It is really as simple as movement requires energy – food (as long as it isn’t a lethal dose of something) will be digested to produce usable energy.
The reasons that McDonald’s is “bad” for most people is twofold:
1) It is calorically dense – a single cheeseburger is like 1/4 of an adult man’s daily recommended calorie intake, and a big mac meal is more calories than most adults need in a day. This is the main reason why “junk” food makes you fat – your stomach gets “full” based partly on volume, and high caloric density means more calories for a given volume.
2) It is pretty empty nutritionally – calories are the simple measure of energy, but there are other nutrients that you generally get through eating things that modern processing takes out of food.
It’s worth noting that for some people, caloric density is *good* – if you are doing a lot of physical activity, you need the extra calories to keep yourself energized. Swimming in particular sees people eat a lot of high-calorie food, because the act of swimming burns a lot of calories, but being submerged in water you use more calories even at rest to keep yourself warm.
So you will burn the calories by walking, but you will have to get your vitamins and other nutrients from other sources.
There is more to it than that, as it turns out nutrition is an extremely complicated thing. But those are the barebones basics.
Bad food is a relative term. A good diet is one where you get enough of everything you need but not too much. And how much you need of each neutrient depend on your body and lifestyle. McDonalds themselves does not make perticularly bad food in many ways. It tends to have a descent amount of vitamins and minerals compared to a lot of restaurant food or home cooked meals. But they tend to have a lot of carbohydrates and fat, of course this depends on the menu items though. Carbohydrates and fat provide your body with energy and if you eat too much the body will store this as fat. Too much fat comes with a lot of health issues. But if your energy requirements are high enough then the high energy meals you get at McDonalds is healthy. You might be surprised at the meals that athletes often consume as these are full of things which are considered unhealthy in the general population.
It is not all good though. The food at McDonalds does also tend to include too much sodium (salt) for a regular diet. Again this depend on the items you buy but on average the amount of salt used in a McDonalds per customer is too high for a healthy diet. If you live in a hot climate, like most of the US, and you live a very active lifestyle then you will need more sodium then average due to all the sweat you produce. This may offset some of it compared to a lazy lifestyle but you should still be careful about getting too much salt if you regularly eat at McDonalds or other fast food chains.
Your body needs a balanced mix of many different types of nutrients. “Macro” nutrients, which includes fats, carbohydrates, and proteins, are the ones that give you energy and build all the components your body needs to maintain itself. You need a large amount of macro nutrients every day, and this amount depends on how much physical activity you do. “Micro” nutrients, which includes vitamins and minerals, are also essential to being healthy, but the amount you need doesn’t change much depending on how much you exercise.
The reason people say McDonald’s is “bad” food is because it provides an unbalanced mix of nutrients. There are too little micro nutrients for the amount of macro nutrients it offers. If you maintain an average level of physical activity and eat only McDonald’s, then you will get too much macro nutrients, which makes you gain weight, and at the same time you’ll get too little micro nutrients, which also hurts your health.
On the other hand, if you do a large amount of physical activity like walking 6 miles every day, then that effectively burns off a lot of calories, which means the amount of macro nutrients you need is much higher than average. In that case, your nutritional requirements actually gets closer the nutritional balance that McDonald’s provides. You’ll make up for the lack of micro nutrients by eating more food in general, and the overabundance of macro nutrients doesn’t become an issue because your physical activity consumes it all.
It really depends on what you mean by “bad”. The main problem with stuff like McDonalds is that it’s very calorie dense…you tend to consume WAY more calories than you actually need.
And, for weight gain/loss purposes, calories is calories…as long as you burn more than you eat, you’re fine. Walking increases how many calories you burn, so can mitigate the potential health implications of eating more calories than you normally need.
It doesn’t do anything for nutritiously questionable ingredients in the food, e.g. trans fats or being deficient in fiber.