The Dose Makes the Poison

01What this is about

You might know the feeling: Monday, you decide — no more sugar, starting today. Two days go fine. Wednesday, there's birthday cake in the office, and you take a piece. And then comes the thought: "screw it, I've already blown it." By evening, the chocolate bar is gone, and the next morning you feel worse than before.

The problem in this story isn't the piece of cake. It's the rule. An absolute ban only knows two states: kept or broken. And once it's broken, there's no orientation left at all. That has little to do with a lack of discipline — and much more with a system that leaves almost no room for real life.

The physician Paracelsus captured this principle back in the 16th century. His original line, translated, reads: "All things are poison, and nothing is without poison; only the dose makes a thing not a poison."

This principle means that almost any substance — even water or table salt — can be harmful or fatal in too high a quantity, while conversely, even highly toxic substances can be harmless, or even therapeutic, in very small doses. That holds for medication — and it holds just as much for your diet.

And yet a whole morality has grown up around food: foods are "clean" or a "sin," you "treat yourself" to something or you "were bad." Talking about food this way doesn't just judge what's on the plate — it ends up judging you. And guilt, in our experience, is a poor advisor for your next meal.

02What the science says

Since the 1990s, nutrition psychology has distinguished between two ways of controlling your own eating behavior: rigid control ("never," "not one bit from now on," all-or-nothing) and flexible control ("less," "mindfully," "I'll go lighter tomorrow instead").

As early as the 1970s, a classic experiment showed how the "screw it, I've already blown it" effect works: people who restricted their eating heavily were first given a milkshake, then allowed to eat as much ice cream as they wanted. The surprising result: after the milkshake, they ate more ice cream than without it — as if the day were "lost" anyway. For people without strict rules, it was the other way around.¹

In a study of 223 adults, flexible behavior was linked to less overeating, lower body weight, and less depression and anxiety. Rigid behavior — such as strict calorie counting and food bans — was, by contrast, more often associated with overeating and higher body weight.²

A study of 106 women who had already lost around ten kilograms showed a similar pattern: women with rigid control were more mentally fixated on food and body shape. Flexible control, on the other hand, predicted a better long-term weight trajectory. The authors explicitly recommend promoting flexible strategies as a result.³

This fits what research tells us about the psychological effects of restriction: people who heavily ban certain foods tend to think about food more, experience stronger cravings, and are more prone to binge eating once their control slips.⁴

One caveat worth noting: many of these studies show correlations, not definitive causes. But the pattern has held up remarkably consistently over decades — and it matches what we see in coaching every day.

03How to put it into practice

1. Replace "never" with "how often and how much." Instead of "no more sweets," try: "something sweet on three days a week, in a portion I actually enjoy."
2. Plan for enjoyment instead of letting it happen on the sly. The piece of cake on Sunday or the glass of wine on Friday can have a fixed place. Planned enjoyment doesn't feel like breaking a rule.
3. Think in frameworks, not rules. When most of your diet is made up of filling, nutrient-dense foods, there's naturally room left for everything else.
4. A slip-up is a data point, not a defeat. The next meal is simply a normal meal again — no compensatory fasting, no extra workout as punishment.
5. Enjoy it mindfully. Sit down, eat slowly, put the phone away. When you eat mindfully, a smaller amount is often enough to satisfy you.

What this can look like in practice

Take Patrick as an example: he loves chocolate and has abandoned countless "sugar-free" challenges. Instead of a ban, he makes himself a deal: two pieces of good chocolate after lunch, at the table, no scrolling on the side. In the evening, there's no chocolate in sight, because it lives in the cupboard instead of on the kitchen counter. On weekends, dessert at a restaurant is fair game too.

The result after a few weeks: those evening "whole-bar-gone" moments become rarer, because chocolate is no longer forbidden — and therefore no longer as exciting. All told, Patrick eats less sugar than during his strictest phases — and feels a lot more relaxed about it.