Fasting & Plant-Based Eating

Two Different Ways of Thinking About Food

Fasting and plant-based eating approach the question of food's environmental impact from entirely different directions, even though they are frequently mentioned in the same breath.

Fasting asks, essentially: when should I eat, and how often?

Plant-based eating asks a different question entirely: what should I eat, regardless of timing?

Combining the two raises an intriguing environmental question worth taking seriously rather than treating as a marketing slogan. Could eating less overall, while also choosing lower-impact foods, produce a larger reduction in food-related environmental impact than either strategy pursued alone?

Why Plant-Based Foods Often Have Lower Footprints

Global life-cycle analyses, including the widely referenced work by Poore and Nemecek covering thousands of farms across dozens of countries, consistently find that many plant-based foods carry substantially lower greenhouse-gas and land footprints than animal products, particularly red meat and dairy, when measured per calorie or per gram of protein.

That doesn't mean every plant-based food automatically has a low environmental footprint, or that all animal agriculture is identical in impact. As discussed in Water Consumption, certain plant crops such as almonds can carry disproportionately high water requirements. And extensively raised livestock on marginal grazing land, unsuitable for crops, is not environmentally equivalent to intensively farmed feedlot beef.

Production methods vary enormously within both categories. But the broad pattern found across large datasets is strong and fairly consistent: shifting the balance of a diet toward plants tends to reduce its footprint, on average, even accounting for this variation.

Where Fasting Adds Something Different

Fasting potentially reduces the total quantity of food required over a given period, as covered in more depth in Fasting vs Plant-Based Diet. Plant-based eating, by contrast, changes the composition of whatever food is consumed, independent of quantity.

Together, the two operate on different axes:

Quantity, plus composition

may be more environmentally meaningful in combination than either lever pulled alone, since one addresses total volume moving through the food system while the other addresses the intensity of each unit of that volume.

Avoiding a False Choice

There is no need to frame the issue as a binary decision between fasting or plant-based eating, as though a person must pick one allegiance and defend it. They address genuinely different aspects of consumption, and nothing prevents pursuing both, or neither, or some partial version of each.

A person might, for example:

• Fast periodically, as described throughout this project
• Eat a predominantly plant-based diet on the days they do eat
• Reduce food waste, a topic covered separately in Food Waste
• Buy appropriate quantities rather than over-purchasing
• Avoid unnecessary consumption more generally, in food and elsewhere

These behaviors address distinct environmental pressures — some relating to total demand, some to production intensity, some to waste and inefficiency further down the chain — and their combined effect is plausibly greater than any single behaviour pursued in isolation.

A Common Misconception

It's worth noting a misconception that sometimes surfaces here: that plant-based automatically means zero environmental impact. It does not. Growing, processing, packaging and transporting plant foods all carry some footprint, and highly processed plant-based products can, in some cases, carry a larger footprint than a simple unprocessed animal product from an efficient producer. The broad pattern favours plants, but broad patterns are not guarantees for every individual food comparison.

The OneYearFast Question

For OneYearFast, this raises an interesting personal experiment that goes beyond the raw environmental arithmetic: does changing the timing of eating alter the way food choices are made when eating does happen?

Anecdotally, many people who fast periodically report becoming more deliberate about what they eat afterward, treating meals as less routine and more considered. Whether that pattern holds broadly, or whether it fades once fasting becomes habitual itself, is an open question.

That behavioral question may ultimately be as interesting as the environmental calculations themselves, because it points toward the possibility that fasting's greatest environmental contribution might not be the calories it removes directly, but the shift in attention it produces around the food that remains.

A Practical Illustration

Consider a simple week of meals. Someone swapping a couple of red-meat dinners for bean- or lentil-based equivalents, while keeping everything else the same, could plausibly achieve a meaningful reduction in their week's food-related footprint, based on the scale of difference typically reported between red meat and legumes in life-cycle studies such as Poore and Nemecek's. Add periodic fasting on top of that, along the lines described throughout this project, and the reductions in quantity and in composition compound rather than simply overlapping.

It's worth being cautious about overstating precision here. Individual results depend on portion sizes, specific ingredients, sourcing and production method, none of which can be captured by a single average figure. The illustration is meant to show the general direction of the effect, not to imply a guaranteed percentage saving for any particular household.

Protein, Nutrients and the Limits of the Comparison

One caveat worth stating plainly: shifting toward plant-based eating raises legitimate questions about protein sources, certain micronutrients such as vitamin B12, iron and zinc, and overall dietary balance. These are nutritional considerations, not environmental ones, and this article makes no claim about what any individual should eat for their health. The environmental case for plant-based eating, on average, is well supported by the research cited here, but translating that average pattern into a specific, sustainable, well-balanced personal diet is a separate task requiring separate expertise.

Key Takeaways

• Plant-based foods generally carry lower greenhouse-gas and land footprints than animal products, based on large-scale life-cycle research.
• Not all plant foods are low-impact, and not all animal agriculture is equally intensive.
• Fasting changes quantity of consumption; plant-based eating changes composition — the two are complementary, not competing.
• Combining reduced consumption with lower-impact food choices may exceed the benefit of either approach alone.
• Fasting may also influence food choice behaviour indirectly, an effect worth as much attention as the direct calorie reduction.