The phrase ‘diet and exercise’ is so common it rolls off one’s tongue. Similar to peanut butter and jam. Rarely is one mentioned without the other. One might, therefore, think the two are interchangeable. If you have a poor diet, you can make up for it with being more active. And vice versa. However, over time, we’ve come to realize you can’t outrun (or out-exercise) a bad diet.

Exercise and Weight Loss

Much of the hype of exercise compensating for a bad diet comes from their joint role in energy balance. Exercise uses energy (burns calories), while diet provides energy. People will often say they just need to get back to their exercise routine to lose weight. Given their opposite roles in energy balance, it seems reasonable that if you ate too much, you could make up for it by a longer workout. But the reality is much different.

Most of the calories you burn are used to keep you alive. If you were to do nothing but lie down, you would burn somewhere between 1500 to 2000 calories. These calories are used for your breathing, beating heart, brain activity and other organ functions.

In comparison, daily activity and exercise use very few calories. For example, a half hour walk burns about 100 calories. In food terms, 100 calories is an apple, banana or 1.5 slices of bread. While four hundred calories is one cup of yoghurt, one cup of berries and two eggs. But a Starbuck’s grande Frappuccino or a single brownie can also have 400 calories. This would require an hour of running to use that many calories.

However, this assumes all those calories used for exercise add up at the end of the day. Meaning, if you ran for half an hour, you would use up 200 calories. But that doesn’t seem to be the case. Our bodies compensate for the exercise calories such that only about 72% of the calories we expect to burn are actually ‘extra’ for that day. This is believed to happen because the human body reduces its metabolic rate throughout the rest of the day.

The Benefits of Exercise and Healthy Nutrition

Despite exercise not being a good mode for weight loss by itself, it’s still an essential part of a weight loss program. Exercise prevents muscle loss and keeps your metabolism higher. When you start eating less, your body doesn’t like that and may lower your metabolism, so you end up losing less weight than you expected. Keeping up with exercise helps prevent this and results in greater weight loss in the long term.

In addition, the value of regular exercise and a healthy diet go far beyond that of burning and providing calories. Both are proven ways to prevent and treat diseases such as diabetes, depression, osteoporosis, heart disease and certain cancers. And also reduce your chances of an early death. The evidence is so clear they are included in numerous disease prevention and treatment guidelines worldwide.

Exercise and Diet are not Interchangeable

Both exercise and diet improve health by altering various disease risk factor such as lowering blood sugar, blood pressure and cholesterol. But the ways in which they do it are different. For example, exercise raises your good cholesterol (HDL-C) but doesn’t do much for your bad cholesterol (LDL-C). Conversely, eliminating trans fat in your diet will lower your bad cholesterol and may raise your good cholesterol.

The same is true for many other risk factors and diseases. But again, the way (or mechanism) by which diet and exercise do so are different. A healthy diet provides the calcium (and other nutrients) needed for bone growth. While activity and exercise stimulate the bones to grow stronger.

Regular exercise also does something diet can’t do—improves one’s fitness. Having a high fitness level is one of the strongest predictors of increased lifespan. That being said, when exercise and diet were studied together, those people who exercised the most and had the healthiest diet had the lowest chances for early death, heart disease and cancer. Being active but having a bad diet or having a healthy diet and being inactive were not as beneficial.

Therefore, for optimal health, you need to regularly exercise and have a healthy diet, as the two are complementary, not interchangeable.

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