Planetary Diets

Headline Conclusion

Getting to net zero emissions is a matter of willpower.

Read on to understand why.

How does energy consumption affect our bodies?

USDA recommendations for adult men range from 2000 to 3000 calories/day. For similar levels of activity, one can therefore expect that on the low end of this caloric intake one’s body weight will be less than on the high end.

At 2800 calories/day, Bob’s energy consumption is balanced by the energy needs of his body. Bob maintains a stable, healthy weight. For Bob’s level of activity, age, and physical stature, the relationship between his energy consumption and body weight is as follows.

Table 1. Bob's Equilibrium Body Sensitivity (EBS)1

Calories/day Body Weight [lbs]
2800 180 (Bob's baseline, healthy weight)
3000 200
3500 240
4000 280

Table 1 refers to Bob’s Equilibrium Body Sensitivity (EBS). This means that if Bob maintains a diet at one of these caloric levels, for a “sufficiently long time,” that he can expect his weight to eventually rise to and stabilize at that level. Just because Bob’s eating a 4000-calorie diet does not mean he will weigh 280 lbs. It only means Bob will eventually weigh 280 lbs if he continues to consume calories at this rate for a sufficiently long time.

Bob goes to a company party and eats a few too many donuts. Yum yum. For one day his caloric intake spikes to 4000 calories. What happens to his weight? Does he instantly weigh 280 lbs? Has he committed himself to eventually weigh 280 lbs because of this one day of “sin”?

There is another rule of thumb, based on energy budgets, which states that a person needs to eat 3500 calories more than they burn off to gain 1 lb. Considering that 2800 calories/day is Bob’s baseline caloric intake for maintaining a healthy body, eating 4000 calories for a single day means eating 1200 calories more than his body needs. This would result in Bob gaining 1200/3500 = 1/3 lb. Energy budgets equate total calories consumed with total expected weight gain. This is a more immediate effect.

Bob’s weight gain of 1/3 lb is based on what he’s done (i.e, ate 6 donuts more than he worked off), whereas the weight to which he stabilizes is based on what he is doing (i.e., eating 6 donuts/day more than he works off).

Is Bob’s weight destined to increase by 1/3 lb, no matter what, because of his donut binge? No. Bob could exercise for the next six days after his donut binge, burning 200 calories/day in exercise, which increases the calories his body burns. That would take care of those 6 donuts.

It’s easy to see why health management is a difficult business. Eating 6 donuts/day is easy and enjoyable and can be done while comfortably relaxed in an overstuffed chair watching a movie. Exercising requires discipline and exertion.

Unfortunately, Bob liked the donuts so much, that he started eating 6 donuts/day on a regular basis, increasing his energy consumption to 4000 calories/day. After maintaining a 4000-calorie diet for 6 months, his body weight increased to 240 lbs. If he continued for another 6 months, he would reach 280 lbs. But after seeing his weight increase to 240 lbs, and already feeling health effects of his daily binging, he decided to cut his donut intake by half, dropping his energy consumption from 4000 to 3500 calories/day. What happened?

When Bob dropped his energy consumption to 3500 calories/day, his weight stopped increasing and stabilized at 240 lbs. Even though he ate a 4000-calorie diet for six months, because his weight did not have time to stabilize at his 6-donut/day regime, once he reduced his energy consumption, he stopped gaining weight. That is, eating a 4000-calorie diet only committed his weight to increase to 280 lbs if he continued at that level for a sufficiently long time.

But Bob really misses those donuts, and so he hatches another plan. Start eating fruits and vegetables! They are healthy, and he’s heard that people who eat a lot of fruits and veggies are generally healthier. So, he returns to his 6-donuts/day plan, and to that adds a bunch of daily fruits and veggies. But after 6 months of eating fruits and veggies, his weight has not stabilized: it is still increasing! Why?!

Because his energy consumption is still 4000 calories/day. What Bob did not understand is that supplementing his diet with fruits and vegetables won’t help him lose weight. To do that, he must reduce his energy consumption to 3500 calories/day. The best way is to substitute some of those donuts with fruits and veggies and not just supplement his donut-diet with fruits and veggies. Eating donuts is easy. Eating fruits and veggies is easy. Replacing donuts with fruits and veggies is not so easy

How does energy consumption affect our environment?

During the development of modern civilization, the equivalent of a 2800 calorie diet has been optimum for healthy functioning of Earth. We are currently eating a 4200-calorie diet, which is increasing 25 calories/yr. As of 2022 our planetary condition is tolerable, but showing health effects of our binging.  Many experts fear that a sustained diet in excess of 4500 calories could eventually cause crippling, irreversible health effects.

Earth has already stabilized at what corresponds to a 3600-calorie diet. But our current 4200 calorie diet means that we are committing Earth to increasingly severe health effects. What should we do about this situation? Should we go on an energy diet, switch to fruits and veggies, or start exercising more?

Organizing an effective diet takes time and effort, so that it is likely that our energy consumption will continue to rise for some time, even as we begin to prepare for an energy diet. And it is likely that the health of the planet will continue to degrade while we get organized for this diet. Earth has adjusted so far to a 3600-calorie diet. Our goal is to reduce our energy consumption so that Earth eventually adjusts to no more than a 4000-calorie diet.

Can you imagine if we let our energy consumption increase to the equivalent of a 5000-calorie diet?

It’s time for that diet we’ve been talking about for so long! Is there anybody who can help us chart a course towards a lower-energy lifestyle?


1. The correlation between daily caloric intake and steady-state weight is more complicated than presented here. For the purpose of this analogy, we assume that a higher-calorie diet results in a person’s weight stabilizing to a higher weight over a period of time. Whether or not the description in this analogy of the relationship between caloric intake and stable weight is scientifically accurate, anecdotally it is what I’ve experienced and many people I know.

Posted by Evan on Monday, 23 May, 2022

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