How Many Calories should You Eat in a Day

So, we all know that in order to lose some weight we need to make changes to our diet. That change usually means cutting something out like calories. If cutting calories is the goal how many should we cut? For instance should a 250 pound guy who wants to lose weight eat the same amount of calories as a 150 pound gal? How many calories are too much, how many is too low? Is there a minimum of calories I should eat? Is there a benefit to cutting out more or am I just spinning my wheels? All of these are good questions.

Let’s start with this; a pound of fat is equal to 3500 calories. That means in simple terms if you eat 3500 calories less in say a week you should lose 1 pound. That is equivalent to cutting back 500 calories per day, but how many calories can you afford to lose. 80% of your required calories are used by the brain, other organs, respiration; chemical processes etc. to keep you alive, the other 20% are used by your muscles. Several studies have shown that the healthful bare minimum for any adult is 1200-1500 calories per day. Going below this for anything more than a few days is detrimental to your health.

Metabolic Testing

There are ways of measuring your metabolism to get a more definitive metabolic rate. The easiest and cheapest is a calorimetry test. You breathe into a mouthpiece while reclining in a chair. The test takes 15-30 minutes and then gives you your RMR or resting metabolic rate. That’s the amount of calories you burn while in a sedentary state.  To get your total caloric daily burn activity levels and body mass must be factored in.

The next test VO2 max (measures your oxygen uptake during exercise) needs to be done in a clinical setting and requires you to breathe into a mask while doing cardiovascular activity. The test progressively gets more difficult until you reach your max. Your utilization of oxygen and production of carbon dioxide is measured.  This allows the practitioner to estimate your caloric burn.

The third test is a lactic acid threshold test. Lactic acid is produced in response to intense physical activity. During this test blood is drawn at intervals as the exercise activity increases. This test is done in a medical setting. The VO2 max and lactic acid threshold test are complicated and expensive. They are also only a snapshot of your current levels. Changes to activity levels or body mass can yield different results.

A simpler Way

A simpler way to approximate how many calories your body needs for maintenance and therefore weight loss is at hand. According to Harvard Medical School and Washington State University a person with moderate activity (30 minutes of exercise a day) should consume 15 calories per pound of body weight to maintain their weight.  So, for instance you weigh 200 lbs. your maintenance calories are 3000 per moderately active day. If you weight 150lbs. your maintenance daily amount is 2250 calories. Sedentary individuals should aim for 13 calories per pound while the heavily active (1-2 hours of intense exercise) should aim for 18.

Armed with his information we can see that a 200 pound  moderately active individual would need to eat 2500 calories a day to affect 1 pound per week of weight loss while a 150 pound person would eat 1750 calories.

So, how many calories are you going to cut out? Cutting 1000 calories a day is surely faster weight loss than 500 calories a day, but it might be less effective. Cutting 250-500 calories a day is relatively easy and doesn’t require major lifestyle changes and still adds up to 26-52 pounds lost in a year.  Cutting 1000 while faster is harder to adhere to as it requires greater life changes and if you fall off its harder to get back on. My suggestion is to start easier then tighten it up a bit at a time.  Another down fall of cutting too fast is a reduction in your metabolism and an increase in the release of appetite hormones; sorry that’s just how we are wired. Go too low and you may indeed be needlessly spinning your wheels. Whatever you choose just remember 1200 calories is the absolute minimum with 1500 more appropriate for men.

Thermic effect of food and other mitigating circumstances

Not all calories are treated the same by our bodies. Some foods have a higher thermic effect (releasing more energy as heat) than others. For instance the body utilizes more calories in protein metabolism (mastication, digestion, utilization) than it does with carbohydrates. Spicy foods are known to increase heat production as well. One more consideration is that higher fat lower carbohydrate diets account for a significant increase in caloric burn, up to 250 calories a day and still more in insulin resistant individuals.  

The bottom line is next time you want or need to diet rather than following some random plan use the Harvard formula to get your estimated requirement as a starting point and then reduce calories minimally from that. Over time once you have established a pattern you can cut back more and or change your macro nutrients values (fats, proteins, carbohydrates) to suit your needs.

References:

Health.harvard.edu – staying-healthy/calorie-counting-made-easy

Healthline.com/nutrition-how-many-calories-per-day

Mayoclinic.org/healthy-lifestyle – Metabolism and weight loss: How you burn calories

Healthyeating.sfgate.com – Recommended calories to maintain weight

Healthline.com/health – What is metabolic testing?