The M3 theory of weight regulation, or, no silver bullet for weight loss.
Sometimes ideas that have been floating around in your mind suddenly fall together. This seems to be one of those cases. The trigger might have been a recent report by Herman Pontzer and 83 others, who studied 6421 people and found that metabolism peaks at ages 2-5, plateaus during adulthood, and then slowly declines after about age 60.
What makes a model too complex?
M3 stands for "multifactor, multimodal, metabolic". Weight management is under the control of a multitude of different factors; it's a complex system that can be purturbed in a large number of ways, and the elements of the system are linked by an equally large number of feedback control factors that make predicting the magnitude of the ultimate effect of any single purturbation is very complex.
It's obvious that complex systems like this cannot be communicated in the simple concepts and language that popular journalists are obligated to use if they intend to engage successfully with a large audience. It's less obvious, but still likely, that public health officials, who wish to issue guidance that can be followed by most people, but who attempt to base their guidance on the best scientific knowledge, cannot effectively synthesize that knowledge in consumable form, even if they had an adequate scientific model.
Today's insight is that an adequate scientific model may be impossible to obtain, because the technology currently used to manage scientific knowledge isn't up to the job. Scientific knowledge advances one publication at a time. But it's cumulative only in the way that termite mound or beehive is the result of myriads of individual contributions from individual termites or bees. The mound does not respond to external stimuli on the same time scale as the stimuli themselves. When new scientific knowledge about a complex model appears, it does not update the model until a new textbook is written that includes the new or revised item. Figures and equations in textbooks are not executable models, they're representations that allow readers to build executable models in their heads or in computers.
And it takes executing the model to determine whether any proposed intervention will result in a desired outcome. If the model is too complex to be operated in your own head or on your own computer, it's not a useful model for managing the system, even though it may be true. The best that can be done is to measure how accurately the usable models work at each timescale, and to track how they improve as more compute power is applied to them, and whether they're improving over the years. Tracking improvements in forecasting accuracy is done in meteorology, and practically nowhere else.
The simple model
Every time a discussion of a new "breakthrough" in weight management is announced, someone inevitably pipes up with "it's easy: calories in minus calories out. It just takes will power, you lazy wimps." Not only is this insulting, but it's wrong. Calories are a measure of energy, they don't convert to mass except in high energy particle accelerators. The weight management fundamentalists should be talking about grams of carbon, not calories. And they need to talk about rate of carbon in minus rate of carbon out.
The same bathtub analogy that is used for climate warming works for weight management. Suppose we have a bathtub with a drain that can't be shut off completely, but can be opened up to allow more flow beyond that basic level. That basic flow represents the body's base metabolism used for simply keeping you alive, and the rest of the flow is what's consumed by other daily activities. The bathtub also has a faucet whose flow represents the contents of the food that is eaten every day. We want to regulate the amount of water in the tub, so that it doesn't overflow or get so heavy that it falls through the floor.
This model is already difficult to manage, since we can easily measure only the weight of the tub and the rate of flow into it.
Calories are a very imperfect measure, since they are an imperfect proxy for carbon. Calories are measured by burning a substance and measuring the amount of heat produced in excess of the amount of heat needed to ignite it. Since food is made of carbohydrates and proteins that contain both carbon and hydrogen, some of that heat comes from burning the hydrogen, and the amount from carbon that we're interested in must be estimated from a chemical analysis of the food. And because some of the measured calories come from sources that are not well digested, such as fiber, calorie measurements overestimate the amount of carbon that becomes bodily tissues to contribute to obesity even more.
The M3 model components
If it's too complex for all of science to deal with, it's too complex to describe in detail here. We can just give a top level outline of its key components. We can't even list all the linkages between them. All the components and their linkages form a graph structure, and computer modeling systems that convert graph structure descriptions into executed model runs don't exist, as far as I know. So anyway, here's a short list:
- Inputs
- Input controls
- Appetite - external sensory
- Mouth feel
- crispy
- crunchy
- chewy
- temperature
- Flavor
- salty
- sweet
- savory (umami, MSG)
- smell - hundreds of qualities
- associative learning
- Hunger - internal sensory
- blood sugar
- stomach fullness
- internal processing
- digestion efficiency
- glucose production
- glucose consumption
- insulin-controlled conversion rate
- tisue targets
- Outputs
- breathing - CO2
- base rate
- exercising rate
- exercise level
- excretion
A better list would attach to each item and link a citation to the scientific literature that provides evidence for its properties.
New frontiers in weight control
The silver bullet would be to identify a single item in the list above that is both measurable and controllable, so that you could manage your weight by controlling that item. But this is impossible, because there are always at least two paths between input and output at any stage of control and processing. Calories are a single measurement, but because the nutrients that provide calories (and their associated carbon) have different rates of utilization (glycemic index) and bioavailability (fiber does not get converted to energy or weight), it's an incredibly unreliable measurement.
Any combination of measurements and controls is even harder to manage and analyze. What we ideally need is an artificial intelligence system that tracks a bunch of nutritional properties and identifies an optimal combination of them to maximize flavor while maintaining a target weight. And it needs to be frictionless and transparent at the same time, quietly looking over your shoulder whenever you attempt to eat anything, computing how it will affect your weight management plan, and gently suggesting alternatives. Alas, this is well beyond the state of the art in AI technology. Training the machine learning part of such a system would take not 6000 participants, but 600,000 of them or more, each tracking every meal and a host of metabolic indicators.
The latest trend in public health interventions to manage an obese population is dietary sugar, and in particular sugary drinks. Sugar is a powerful contributor to weight gain since it's both calorie dense and is metabolized very rapidly. It makes a big contribution to the rate of carbon input to a person's mass flow balance. So regulating sugar input by public health officials might have some impact.
Focusing on the appetite component of the M3 model offers additional possible opportunities for management. One of appetite's most dangerous properties is that it's insatiable. It's not for nothing that Lay's Potato Chips once had a slogan "Bet you can't eat just one." Eating something that's crispy, crunchy and salty doesn't satiate, it increases the desire to eat more.
How this works is very unclear, and may be beyond the capability of current neurophilosophical thinking to clarify. Super-appetizing foods have biased, if not overridden, the free will of a large fraction of the human population. Philosophers arguing over whether free will exists amazingly fail to take facts like this into account. A will that is partially free and can be biased or overridden is incompatible with the content and methods of these arguments. Simply saying that these foods have been engineered to be addictive, as many writers assert, merely assigns blame without explaining the phenomenon.
But if you can't control the desire for salty snacks, you can at least improve the food value of them. Instead of starchy chips and puffs that are metabolized vary rapidly, you can choose snacks with more protein that is metabolized more slowly, such as pork chicharrones, and ones that contain more fiber that is not metabolized at all. It's something to look for in the grocery store.