How Many Calories Do You Need A Day
In yesterday’s post we discussed the startling data by the FAO suggesting that Americans on average consume 3,750 calories. This is remarkably high when compared to the 2,000 calories a day considered standard for most adults.
Have you ever noticed the “% Daily Value” footnote beneath a packaged food’s nutritional label? It reads:
“The % Daily Value tells you how much a nutrient in a serving food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.”
What’s a calorie?
A single calorie is the amount of energy it takes to raise the temperature of 1 gram of water by 1°Celsius (1.8°F). A food’s or beverage’s calorie count indicates how much energy it contains.
Calories fuel everything our bodies do. The speed at which we burn them is our metabolic rate. Even when idle or asleep, we use them to:
maintain our heartbeat
regulate our temperature
build muscles and bones
grow hair and nails
think or dream
digest and store nutrients
The Mayo Clinic reports that 10 percent of carb- or protein-based calories go to digesting and absorbing nutrients.
According to one Harvard Health Publishing article, sleeping bodies burn 40 to 55 calories every hour. So, even if we sleep all day we would still burn 960 to 1,320 calories.
The amount of energy (calories) we burn on “automatic” bodily functions is our basal, metabolic rate (BMR). The American Council on Exercise estimates it at 60 to 75 percent of our daily energy expenditure.
We also burn calories with nonexercise activities (aka scientifically as “nonexercise activity thermogeneisis,” or NEAT). Think:
standing instead of sitting
gardening or yard work
washing the car
playing with the kids or walking the dog
Together, NEAT and deliberate exercise account for 25 to 40 percent of our daily calorie expenditure.
Where did nutrition labels come up with “2,000 calories a day?” That’s simply a generally accepted figure — humans, on average, need to consume 2,000 calories of energy each day to fuel their basal metabolism.
In the real world, however, BMR isn’t a one-number-fits-all proposition. Gender, bodily weight, height and muscle-to-fat ratio influence it. (Muscle burns more calories than fat.)
And a single pound of fat contains 3,500 calories. So cutting back by 3,500 calories a week should mean a 1-pound weight loss, week after week… except it doesn’t. Why?
In the Nutritionfacts.org video The 3500-Calorie-per-Pound Rule Is Wrong, Dr. Michael Greger explains it this way:
“… the 3,500 rule fails to take into account the fact that changes in the calories-in side of the energy-balance equation automatically lead to changes in calories out—for example, the slowing of metabolic rate that accompanies weight loss, known as metabolic adaptation.
He gives the example of a sedentary woman weighing 150 pounds who reduces her calories by 500 per day. That’s 3,500 calories per week — enough to drop 52 pounds in a year, if the 3,500-calorie-per-pound rule actually worked.
Instead, he says:
“What would happen is that in the first year, instead of losing 52 pounds she’d likely only lose 32 pounds, and then, after a total of three years, stabilize at about 100 pounds. This is because it takes fewer calories to exist as a thin person.”
By losing 50 pounds, in other words, she’s reduced her body’s workload by one-third, so it simply doesn’t need to burn as many calories.
“Metabolic adaptation” works in reverse, too. Add 500 calories to your daily diet, Dr. Greger says, and eventually you’ll be heavy enough that your metabolism burns 500 more calories to keep you alive and moving each day. And you’ll stop gaining.
It is clear that there are many factors that influence how many calories our body expends in any given day, but there is only one factor that controls our calorie intake and that is what we put in our mouths.
So the big question is, are we consuming the American average of 3,750 calories, or the 2,000 calories the average person needs?
It is much easier to eat 2,000 calories by choosing exclusively plant-based foods. Enjoying fruits, vegetables, legumes, and whole grains is the best way to give our body the calories we need to function properly, lose weight, and lead a healthy lifestyle.