- Dietary restraint means imposing fixed rules regardless of other factors. This is an open-loop system, characterized by instability.
- Self-regulating means operating by rules that incorporate feedback from measurements of relevant variables, in a closed-loop manner.
- Open-loop dynamics are typical of restrictive eating disorders and exercise compulsions.
In Part 1 and Part 2 of this series, I introduced the recovery/all-inclusive vacation comparison and sketched some evidence suggesting that if you (1) have strict limits on eating and (2) are temporarily disinhibited for some reason (maybe you flouted a dietary rule in a small way, or you were in an altered state thanks to alcohol or strong emotion), you may well break your food rules by a wide margin. A range of recent studies adds further support to the general idea that dietary restriction impairs behavioural self-control: for example, a study from last year found that 10 days of calorie deprivation reduces people’s food-related but not other types of self-control (Standen and Mann, 2021).
Rules and Self-Regulation
One way to interpret this type of evidence is that dietary rules prevent effective self-regulation. What exactly do I mean by self-regulation in this context? I guess I mean stopping and starting eating because of a sensitive, adaptable set of instincts, not a rigid and arbitrary set of requirements.
Think of the milkshake drinkers we met in Part 2, who normally exercise high dietary restraint: All they’re doing is applying an input rule, and, once it’s broken, they’re lost. Once some researchers have induced them to have the milkshake, but their rule says not to, then the rule is useless to them because it’s already broken. And so they often end up compounding their rule-breaking by eating significantly more than they would have if the rule to eat less had never existed and (maybe most paradoxical of all) more than if they hadn’t eaten anything beforehand. They do so because (1) they have an awful lot of unfed hunger generated by following the rule, and (2) what the hell, there’s no difference between a rule broken by a millimetre or a mile; it’s still a failure. As soon as the boundary of the permitted is transgressed, there’s nothing left to support the supposedly desirable behaviours and resulting experiences. You’re at sea with your standard compass useless to you.
Closed Loop Versus Open Loop
In structural terms, this neatly illustrates the difference between a closed loop and an open loop. In an open loop, you have a rule (say, eat 2,000 calories a day, or run 2 x 20 minutes a day) and you apply it regardless of changes in state. This may have the advantage of simplicity: You don’t need to make adjustments based on a range of measurements. But it also means that uncertainty about the things that matter gets amplified as time passes. You can’t correct for mistakes, either because you have no idea where you are (because you’re taking no measurements of anything meaningful—e.g., you’re blind to how well or badly your life and health are panning out) or because you’re not acting properly on the measurements you are taking (e.g., because you’re afraid to do anything differently, even though you see how badly what you’re doing is serving you). You have no robustness to perturbations, in your environment or in yourself, because you have no way of even gathering the relevant information effectively, let alone acting on it to reliably counteract instability.
This is anorexia nervosa. The main form of measurement going on that’s allowed to have any appreciable effect on anything is the measuring of the input variable to which the rule attaches (e.g., you measure calories consumed so far today to decide whether to eat any more this evening). Other measuring (e.g., of bodyweight or calories in or out), even if it’s as obsessive-compulsive as the behaviour-guiding kind, probably makes no difference to the application of the rule (you eat/exercise the same regardless of your weight, or you eat the same regardless of your exercise, say). If these secondary forms of explicit measurement do have effects, it's by supplanting any other information you might have gathered about your current state (e.g., feeling tired or unwell, being injured, being hungry).
Thus, returning to the milkshake and ice cream experiment, things get eaten or not eaten depending on (say) a daily calorie rule, and if this rule is prevented from being applied (e.g., some calorie value is concealed from you) or is broken (e.g., overshot because some nasty experimenter induces you to have something all sugary and fatty and unnecessary), the whole thing collapses, because there was never anything else to turn to. As with cruise control that isn’t actually measuring vehicle speed and/or is assuming no disturbances (by road surface, gradient, etc.), the system is fundamentally fragile. It may be stable for a while by accident, but it won’t stay that way for long in the real world.
By contrast, in a closed-loop system, the information gathered is used to determine the next action. For example, say in the open-loop context you have a fixed exercise routine that proceeds every single morning regardless of physical or mental state, location, busyness, etc. The rule (e.g., x reps by y sets @ intensity z) is always obeyed and never changes. In a closed loop, the type, length, intensity, and sheer presence or absence of the routine adjust to all the relevant factors in the organism and its environment. The things being measured are dynamic; the measurements are about assessing the current state in order to be able to act in line with it.
Most of the closed-loop measurements don't even feel like measurements in the numerical sense that explicit rule following requires, because they're automated by evolved biological mechanisms that support performance within acceptable homeostatic bounds (e.g., via ghrelin and leptin secretion, metabolic modulation, force of muscular contraction under load), as well as by automatically introspected inclinations and sensations (anything from musculoskeletal mobility to lethargy to personal/professional priorities for today). All of this is compromised if top-down exercise rules are imposed without acknowledgment of the relevant signals that could prompt self-correction.
In reality, of course, the distinction isn't absolute. The open-loop version doesn’t manage to entirely override all the equilibrium-geared control systems of the human body. It may also incorporate limited feedback, in the form of compensation for some episodes of rule-breaking, though this is still irrespective of the wider causes and effects. Meanwhile, the closed-loop version has rules of thumb, input defaults that mean, in absence of any off-the-charts measurements of other kinds (e.g. serious DOMS [delayed onset muscle soreness], coming down with a cold), the habitual behaviour will occur, within standard bounds. This reduces the cognitive load of having to make every decision from scratch every time. But all kinds of micro-adjustments (e.g., in amount of warmup, rest time between sets, whether to go for your personal best today), are happening more effectively for the fact that the open-loop rules aren’t constantly trying to override everything else.
If you’re operating open-loop, or attempting to, in the realm of food (or any other life domain I can think of), you’re probably not living very happily, even when you’re not transgressing. So, in the penultimate part of the series, we’ll take a look at what your options are if this open-loop state sounds like you, and you’d like it not to be.
Standen, E. C., & Mann, T. (2021). Calorie deprivation impairs the self-control of eating, but not of other behaviors. Psychology & Health. Paywall-protected journal record here.