When it comes to diet and recreational drug use, isn't "all things in moderation" a good rule of thumb? No. In fact, it is pretty much a terrible one. Here's why.
Your health is too important for a simplistic heuristic such as this one. Quick rules-of-thumb are useful in many mundane circumstances such as choosing a line with the fewest people in it at the grocery store or choosing a movie based on the fact that you enjoy similar movies in that genre. However, using a 4 word heuristic for deciding what foods you should eat and avoid, how much and how often, along with what drugs you should use and avoid, how much and how often is about as stupid as choosing a life-partner based on the heuristic "as long as they can cook."
Even a "moderate"* amount of some things can kill you. First let me address the obvious in that we are not talking about "all" things when we say "all things in moderation." This absolute statement includes poisons and "recreational" drugs that have a dangerously high probability of death associated with "moderate" usage. There are clearly things any reasonable person who cares about their life would want to avoid. However, those who boast about being a "try anything once kinda person" will experience far greater social pressure to maintain that image than someone who is committed to making gradual and consistent dietary improvements.
*"Moderation" or "moderate" can end up being synonymous with "way too much." There is no clear amount associated with "moderate," so the person practicing moderation is free to set their own acceptable range based on personal biases and social norms of the company in which the person keeps. We are very good rationalizers and can justify our behaviors to ourselves and others. Our friends, often our "partners in crime" share our behaviors and have little incentive to point out our abuse of the concept of moderation. We eventually find ourselves stuck in our own reality where what we once might have seen as "excessive" becomes "moderate." An example is an often-cited study by Perkins and Berkowitz (1986) on the perceptions of drinking norms on college campuses. They found that students who perceived the norm (often seen as synonymous with "moderate") to be similar to their own drinking behavior, tended to drink much more heavily than the actual norm.
Many substances and foods can be highly addictive. As many alcoholics have learned the hard way, there is no moderation for them when it comes to drinking. Addiction is a disease, and many people have very addictive personalities, meaning that moderation is not a realistic goal for them. And it's not just drugs that people are addicted to; it's the rush of endorphins that accompanies satisfying a craving or appetite. We are all more or less addicted to this rush since addiction occurs on a spectrum.
Intolerance, hypersensitivity, and allergic reactions. Researchers estimate that up to 15 million Americans have food allergies (“Facts and Statistics - Food Allergy Research & Education,” n.d.). Some of these people simply experience annoying reactions, while some end up dead as a result of the reaction. Frequent effects of substance intolerance and hypersensitivity due to "moderate" ingestion of a substance can result in a lower level of well-being.
The combined effects of unhealthy foods. We tend to group things in such a way that works to our short-term advantage and satisfies our instant gratification. While we can say "unhealthy foods in moderation," we can also say Big-Mac's in moderation—and Whopper's in moderation, and Meatball subs in moderation. For example, one Big Mac per week might be considered "moderate," (especially by someone who loves Big Mac's) but when you add a Whopper and meatball sub that same week, then a few other indulgences, you have a very unhealthy diet—although you are technically moderating each individual "group." This is just another way that "moderation" can be a very slippery slope.
The combined effects of harmful substances. As with unhealthy foods, multiple harmful substances taken "in moderation" increases the overall risks associated with the substances. Using a different drug each night might make you a moderate pot smoker, but you would still be a heavy drug user.
People significantly over-estimate their willpower (Baumeister & Vohs, 2003). Willpower is the ability to resist short-term temptations in order to meet long-term goals. Moderation requires willpower—a lot more for some people than others. Believing we have strong willpower when in fact we don't can be very dangerous.
The moderation game is a risky, dangerous, and even potentially fatal one. While an excess of anything is bad ("bad" being inherent in the definition), it is fallacious to think that a moderate amount of anything (especially "everything") is okay. The occasional Big Mac, piece of cheesecake, and snort of cocaine still adversely affects your health. Trying pot just one time still results in an overall negative health effect. This does not mean you need to be a saint or a perfect eater, but you should first be aware of risks and dangers of unhealthy foods and recreational drugs, then balance those risks with the potential rewards to your overall well-being. You choose how you want to live your life, but make that choice being aware of the facts, not being flippantly ignorant of them.
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