Life is not linear, nor is the energy balance.

Updated 6.18.2013; reformatted 9.14.2015
The first clause in the title of this piece was a favorite saying of mine when I was an experimentalist working in a research lab. Linear models (trying to fit data to a straight line for analysis) are the simplest to apply and understand, they also seldom, if ever, accurately reflect the real world. Certainly in terms of bodily function and weight loss, the linear model IS NOT accurate. The second clause is the subject of this essay.

But Wait!

I imagine any reader who's searched this site must be thinking, "You are adamant that weight loss is control by energy balance— so what give?"

Energy balance means energy in vs energy out, most often stated as calories in vs calories out (CICO) because calories are a unit of measure of heat. Calories are an older unit of measure, in modern SI (Systeme Internationale) units energy is measure in joules. In actuality, the "calories" listed on labels are kilocalories or (in SI units) kilojoules, the prefix kilo is dropped. I AM adamant that CICO is the bottom line.

But this does not mean the energy balance is not a linear equation. Most people react as though the equation has the form of y=x+k (which is the equation of a line with a constant slope). But this is NOT the case. Stated simply, the energy balance equation is energy in = energy out + energy stored. If energy in = energy out then energy stored is zero. If energy in > energy out then the excess is deposited or stored in fat cells. If energy in < energy out, then energy stored in the fat cells is used to make up the difference and weight is lost.

Energy In

"Energy in" represents a single number (number of calories consumed in any form, whether eaten or drunk) but the "energy out" side of the equation consists of ALL means of expending energy in the body. Sometimes the energy in total is adjusted to reflect bioavailability during digestion. In the construct that I use here, any effects of bioavailabilty is included in the energy out side of the equation. In my view this makes more sense, because energy that isn't absorbed is excreted.

Energy Out

Here is where the nonlinearity enters! The energy out side of the equation includes a term for the body's basal metabolism rate + a term for energy expended during exercise + a term for energy expended during non-exercise movement + a term for the energy expended to digest food consumed + a term for any food not absorbed and thus excreted. Given this, Energy in = Energy out IS NOT A LINEAR EQUATION!

That's why experiments like Feltham's are worse than nuts they're pointless because he's assuming that energy in = energy out is a linear relationship. It's not, and never was, so all he's doing demonstrating the obvious.

So let's define the terms on the energy out side of the equation.

Basal Metabolism Rate (BMR)

BMR is the amount of energy the body requires to keep you alive if you were in a coma. BMR depends on the height, weight and age of a body AS WELL AS the health of the body. Note: BMR is also called Resting Metabolic Rate (RMR) or resting Energy Expenditure (REE) in the literature.

Height

A shorter adult needs to eat less than a taller adult. This online body weight simulator remains my favorite source for determining the amount of energy required to support a body of a given height and weight. At 59.5 inches tall, I do NOT need to eat the same number of calories as a woman my age who is 69 inches tall.

Weight

A smaller body simply requires less energy to run. Even in a healthy body with a normally functioning thyroid, weight loss will reduce metabolism rate. This is NOT a flaw in diets, it is simply a fact. The rate of weight loss does affect the amount of calories required to maintain the new smaller body, but that is a function of body health, which is discussed below.

Age

Age matters when considering required amounts of calorie consumption. It's a sad fact, but true. As you age, your metabolism will slow as your hormone levels shift. Menopause for women in obvious, but it's becoming clear that male hormones also change with age. You can use the online body weight simulator to see how your caloric needs will decline how you age. Input your current data, then change nothing but your age. The decline in calories won't be much, but given that most older people also move less, it makes a difference.

Health

Health of a body includes endocrine system function, actually it includes ALL the body systems. So (for example) if a body was diabetic, the BMR will be affected. Diet and weight loss have been found to affect metabolism rate because it affects thyroid function,in complicated and not well understood ways. Weight loss is known to reduce thyroid function and thus body temperature, especially on low carb diets. However, any perturbation in the body's systems (such as cancer or infection) can effect metabolism as the body adjusts to the stressor. Thus BMR is generally presented as a "black box" number because it's SO complicated. People simply measure it, and assume it's a constant for each individual. It is not. BMR also responds to all the factors that follow.

BMR is estimated to represent 50-60% of the energy out. It is both the largest and most complicated factor in determining the energy expenditure of a body.

So just to emphasize, the LARGEST factor in the "energy out" term is a function (meaning it's affected by) most of the other factors in the "energy out" listed below. Life is not linear, but that doesn't mean the equation doesn't apply. It just means it's a nonlinear effect.

And with that we'll move onto the other factors included in the energy out side of the equation.

Thermic Effect of Activity (TEA)

The thermic effect of activity (TEA) is the amount of energy used, expended or "burned" during exercise. This is the term that includes any trip to the gym, yoga class or jogging. The size of this term obviously depends on how often and how vigorously you exercise.

Note: TEA is also called Exercise Activity Thermogenesis (EAT). I prefer TEA.

Non-exercise Activity Thermogenesis (NEAT)

Non-exercise Activity Thermogenesis (NEAT) includes all the moving the body does outside of the formal exercise measured by TEA. NEAT, in my view, is vastly under appreciated by dieters. Most dieters look to maximize their TEA terms, which is all well and good, however, more than one study has shown that in response, the body subconsciously minimizes NEAT. In contrast, in my own weight loss journey, I have worked to maximize NEAT. Of course, I also exercise, but the lion's share of my effort has been to make sure that my NEAT levels increase. So that I don't get sidetracked here I'll just note that the simplest way to increase NEAT is to STAND UP.

Note: NEAT is also called Spontaneous Physical Activity (SPA).

Thermal Effect of Food (TEF)

The thermal effect of food (TEF) is the amount of energy the body expends to break down the food that you eat so that nutrient can be absorbed. The amount of energy required to breakdown a piece of food depends on its macronutrient (carbohydrate, protein or fat) content as well as how it's been processed. Carbs require little energy to broken down, protein requires much more, which is, in part, why protein provides a greater feeling of satiety. Fats are not broken down, they can be stored as ingested.

Generally, the more processed (ground, cooked etc) that a food is, the EASIER and MORE COMPLETELY it is absorbed. For example, more of the calories in a tablespoon of almond butter are absorbed than the calories in a handful of whole almonds. This is why so many diets prescribe eating whole foods and avoiding highly refined packaged or industrially processed foods.

TEF is estimated to be 10% or less of the total daily energy expenditure (TDEE), and yet much of the arguing in the diet blogosphere revolves around TEF. The fact that protein requires more energy to be broken down results (or so low carb advocates would have you believe) in a metabolic advantage for high protein diets. But in the end, all the durm and strang is about no more than 10% of the total.

Excretion

Excretion includes solid (fecal), liquid (urine), and gaseous (breath) waste elimination of any food remnants from the body. Anything that isn't absorbed is excreted, one way or another. The amount lost through breath is generally small, unless you're in ketosis and have the halitosis that is associated with low carb dieting. I include breath it only for completeness.

As noted earlier, the excretion category is where any differences in bioavailability would be included in my model. Excretion is highly individual (and highly personal!) and obviously varies with diet as well as chewing efficiency. Foods that don't breakdown well or completely (corn kernels, nuts) will pass through and be visible in your stool, especially if you don't chew your food very well before swallowing.

Energy Stored (or released)

The amount of energy stored (or released from fat stores) depends on the difference between the amount of energy (measured in calories) consumed and the amount of energy expended (measured in calories). If what you eat is less than what your body used in all of the categories listed above, energy is taken from body stores (fat cells, glycogen stores, etc). If you've eaten more than your body needed, then the body stores whatever isn't excreted.

The Bottom Line

Hopefully at this point it is transparently obvious why the energy balance is NOT a linear equation. So all of these "n=1" efforts to disprove CICO are meaningless. The energy balance DOES apply, just not in a linear fashion. If you are in an energy surplus (eating more than you expend), over time you will add weight. If you are in an energy deficit (expending more than you intake) over time you will lose weight.

It's called an energy BALANCE for a reason.

The real question is, how large is the energy excess, and how does the body respond? If by cutting your intake hugely results in your body lowering your BMR or NEAT, then you are NOT in as large a deficit as you think. The body tries to maintain homeostasis or equilibrium in body function.

Lowering intake disrupts this balance, and the body responds. The greater the perturbation to the system, the greater is the reaction. Starving yourself causes the body systems to react more than simply eating a bit less and moving a bit more. That's why slower weight loss results in less metabolic shift. It's also why NEAT is the secret weapon of weight loss.

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