The Real Problem with Calories In Calories Out

The Real Problem with Calories In Calories Out December 30, 2023

Is “Calories In Calories Out” the reality about weight loss and obesity? I caught a few glimpses of the recent Twitter food fight over that question, and here are the two main, credible arguments in favor:

  • It is a mathematical fact.
  • We understand that many people find the math hard, so they use other rules that are simpler to follow, and that’s fine, but it’s still CICO.

I’d like to weigh in with a reality check: CICO is sometimes the problem, but it isn’t always the problem.

I know real live people who used calorie counting, either directly or through a simple set of portion-control practices, to lose weight and keep it off. Some included exercise in their approach, others did not.  Most experienced a little bit of hunger while losing weight, but overall found it to be a manageable experience with no negative side affects (no depression, anxiety, anger, fatigue, frequent infections,  hormonal disorders, etc.)  After reaching their goal weight, they had no further difficulty with maintaining their new, lower weight via continuing with the same dietary approach that got them there.

These people exist. They are by no means the majority of dieters, but they are real human beings in actual human bodies, and they are the examples the public health industry points to when saying that Eat Less Exercise More is all it “really” takes.

And yet, clinical practice has shown that while CICO is sometimes an effective approach to weight loss, most of the time CICO alone is not sufficient.

What’s going on?

Let’s pause for some metaphors.


If you google “Causes of Foundation Failure” overloading is often (not always) on the list.  The structure is too heavy for its foundation, done. That’s the problem.

Dam failure? Maybe there is simply too much water pushing against the dam. You need to either reduce the amount of water being retained, or you need to strengthen the dam, or both.

Power grid going down? Maybe there is too much demand for electricity and the system can’t handle it.

Blew a circuit in your house? Maybe you’ve plugged too many appliances into that outlet.

These are real things that happen, and they are analogous to Calories In Calories Out. Your foundation really will fail if you overload it. Your circuit really will blow if you overload it. It’s not pretend.

And yet I promise you: Do not hire an engineer whose only solution is, “I guess three bedrooms is too much house for you,” or “Have you considered that maybe you’re just not meant to have lights in that room?”


Sometimes the problem is simple, obvious, easy to diagnose and fix.

I know to unplug the portable heater in the bathroom before running the hair dryer and we’re set. The circuit can only take so much. No big deal. Nothing deeper going on.

Likewise, I have a friend who lost all his excess weight just by cutting out his ice cream snack at bedtime and going for a pleasant walk every day. Simple, painless, and while we could point out that dropping the sugary item and increasing the exercise both have a favorable effect on insulin levels, which is essential to metabolic health, we can at least grant that it’s entirely possible simple calorie balance was the problem.

But no amount of “don’t overload the foundation” will fix the fact that your house is on a sinkhole. No amount of “eat less exercise more” will fix your weight problem if you have an underlying issue above and beyond simple overeating.


There is a reason that for many people, net-calorie reduction alone is not an effective weight loss strategy.

This happens either because:

  • They were already eating a healthy quantity of food, and their overweight was driven by some other problem than simple energy balance.
  • Their body responded to the calorie reduction by going into a powerful “starvation” mode — decreasing calories-in caused an uncontrollable drop in calories-out as the body fought against the perceived famine.

In both cases, calorie reduction is not a healthy weight loss strategy.  

People in these situations need to figure out a different approach to being as healthy as possible, given the body that they have.


A lot of people who can’t lose weight through simple net-calorie reduction can lose weight successfully either through a fasting protocol or through changing the composition of their meals — even if in all three approaches they are eating the same total number of calories.

This is because though the number of calories may be identical, how you feel and how your body responds can be remarkably different.  A successful diet has to both:

  • Be mentally sustainable. If it leaves you light-headed, fatigued, or experiencing serious psychological side effects, it’s not sustainable.
  • Induce a healthy metabolic response.

Thus there’s a reason that some people try a diet that works great for their spouse, and the diet fails. Either it causes too many unhealthy side effects, or the diet itself is entirely manageable, but no weight loss ensues.  I’ve known people who simply had to try a different diet than their spouse, and the different diet worked miracles!

It’s like husband and wife had different bodies! They were not the same! They had different biological problems.


I have a daughter who is considering becoming a poop donor. Results of research into fecal transplants as an obesity treatment have been mixed — sometimes it leads to weight reduction, other times it doesn’t.  This anecdote of a fecal transplant (for other reasons) apparently causing obesity is quite telling.

I think based on the research to date we can reasonably conclude that sometimes gut microbiota is the primary factor in obesity or leanness . . . and other times it isn’t.


So, in conclusion:

Is it true that eating too many calories will cause weight gain.

It is not true that all weight gain is caused by too many calories.

It is also not true that everyone is able to gain weight by eating more! Some people have serious medical problems causing their low body weight. Other people have not-necessarily-pathological reasons that they simply can’t eat enough to gain weight because the sheer amount of food it would take is not tenable.

Thus I conclude: Of course you should consider whether you are simply eating too much.  But also the human body is complex and there are many factors that drive body weight.

If you’ve resolved to “finally lose that weight” this year, or if you’ve given up on losing that weight because your resolution has failed so many times in the past, consider that you might need to do a lot of research to figure out what’s going on.

Crepes and cider at a restaurant near Notre Dame, Paris.

Photo (by me): Pretty good crepes and cider at a restaurant near Notre Dame Cathedral, Paris, France, 2018. This is not an effective weight loss protocol for me.

About Jennifer Fitz
Jennifer Fitz is not nearly as overweight as she could be, and that is because she puts a ton of effort into figuring out how to make good on the genetic hand she's been dealt. But alas, sugar is the enemy and that is no fun. You can read more about the author here.
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