All weight loss diets work on a single premise — to eat less than your body requires to fund daily movement. Your body will tap into your fuel stores to keep you functioning, like withdrawing money from a bank account to pay your bills. The more you withdraw without depositing more, the smaller your bank balance (and, in this case, your fat stores) will be.
From a pure calorie deficit argument, no diet is the best. All methods are roads that lead to the same destination. However, I will tell you the one that I find, from my experience, is troublesome — and that's calorie counting.
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Our bodies use energy derived from food to perform our daily functions, and how we measure this energy is in the form of Calories (C) or kilocalories (kcal). According to an article titled How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods? published in Scientific American, an item of food is placed in a sealed container called a ‘bomb calorimeter’ and entirely burned while simultaneously heating water. The amount of energy the food contains is, therefore, how much is required to heat the water to 1 degree Celsius. Although we primarily reference "calories" in food, it's more accurate to call them "kilocalories" (kcal) or referenced as kilojoules (kj)
It sounds rather scientific and precise. However, scientists realize that's hardly the case for a staggering number of reasons.
The first thing to calculate is how many calories your body burns. Any Google search will bring up roughly the same result: men should have around 2,400 kcal per day, women, 2,000 kcal per day. These numbers are derived from a mathematical formula; the most common one is the Harris-Benedict Equation which calculates age, weight, and height and uses a multiplier for your activity level.
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However, no matter how sedentary you may be, our bodies are adaptive creatures and will make dynamic decisions on how many calories it needs to burn for your survival.
For example, according to the Sleep Foundation, even one night of disturbed sleep can lower your calorific burn the following day, sometimes a reduction of up to 20%. It also decreases our energy for exercise, so we burn fewer calories at the gym, which can cause a dramatic reduction in our calorie burn.
Furthermore, women's calorific needs change throughout their menstrual cycle, sometimes requiring an increase of ~164 kcal during the luteal phase.
Being highly stressed can result in a higher level of cortisol, which has an awful habit of chewing up muscle as fuel, resulting in lower muscle mass. Muscle mass is costly to keep in our bodies and requires many calories to keep it functioning. The less muscle you have, the fewer calories your body needs.
These are just a few of the survival mechanisms to ensure you don't damage yourself with poor habits that work against your survival, and as a result, we need help to pinpoint our exact calorific burn.
Furthermore, to lose weight, we need to reduce our daily calories to allow our bodies to use our stored fuel, which is often between 250-500 kcal for sustainable weight loss (~.5-1 lb per week). Given the information I've listed above, this is like shooting a dart at a dartboard with a blindfold. But it only gets more complex.
When looking at the calories found in food, you'll discover that even natural foods differ wildly in their calorie makeup, different cooking methods alter the digestibility and absorption of calories, the margin of error of calories listen on pre-packaged foods, and our inability properly gauge portion sizes.
You'll know this pain if you've ever used online calorie trackers. Try looking up the humble apple — often, you'll see a generic apple of 100g (USDA) kicking around the 52-kcal mark, and some apples will hover over 104 kcal per apple (VeryWell Fit). The discrepancy in this food alone is about 52 kcal — but it’s also whether or not we notice the serving sizes are different. Is 100g considered a small apple? Which one do you choose? And it's not just the apple. For interest, try plugging in items like "sweet potato" and see what you find out.
Your chosen cooking method changes the digestibility of your food, meaning that some cooking methods break down proteins or fibers, making them more accessible. Foods like meat and starchy tubers commonly fall into this category; imagine eating meat raw or not cooking your potatoes. As reported in a study referenced in the Proceedings of the National Academy of Sciences, cooking your food increases the number of calories available for absorption by breaking down fiber and protein during cooking. According to this study, cooking does some digestive processes for us, meaning that we burn fewer calories digesting cooked food than we would if we ate more raw foods. The same happens to a lesser degree when you cook vegetables, but blending and grinding foods (think of food items like peanuts versus peanut butter) do our digestive work for us. Therefore we absorb more nutrients through the final product than we would if we ate the food in its original form.
But these differences so far can be minimal, perhaps not enough to make a seismic shift from being in a calorie deficit to suddenly being in a surplus.
Food labeling organizations, such as the USFDA, allow a margin of error with energy labeling of up to 20%. That means if a product falls on the highest approved margin of error of 20% from the listed value, a serving size that indicates there are 250 kcal could have up to 300 kcal. It's starting to add up.
And this leads to my final point — humans are notoriously optimistic about their ability to eyeball a portion size without a weighing scale accurately. We often err on the side of excess rather than what is actual portion size, and a perfect example of that is watching someone accurately judge a portion size of peanut butter or cheese. An ideal portion of peanut butter is about the size of your thumb, a piece of cheese the size of a matchbook.
Calorie counting can be a great way to educate people about the calories found in their foods, and it's a significant first step to bringing awareness to your diet. However, we can't live and die by these numbers alone because they are simply inaccurate.
There are two ways that I coach people into better eating practices that will enable them to lose weight. The first is to tune into their hunger and satiety signals, to learn when their body tells them they are feeling satisfied or hungry and eat accordingly. Sometimes this means palpating the stomach several times daily to connect with the hunger and physically full signals. Next, eat until “satisfied,” not stuffed. By listening to your body’s needs, you’re adapting alongside your body, not forcing it to conform.
The second way is to learn how to eyeball portion sizes, which can be done using the Hand Size Portion method. A portion of protein is the size and width of your palm, cooked carbohydrates and fruit fit into a cupped hand, vegetables should make up the size of your fist, and fats should be the length and width of your thumb. Women can start with one portion of each, and men will have two. Then, by zoning into their hunger, you can change this ratio by eating more carbohydrates on days with intense exercise or including more protein and vegetables if you don't feel satisfied with the originally recommended portion.