Effects of Diet Choices on Animals

For a French translation of this page, please see Répercussions de nos choix alimentaires sur les animaux.

For a Spanish translation of this page, please see Consecuencias que tienen nuestras decisiones en la alimentación sobre los animales.

Many animal advocacy organizations seek to reduce animal suffering and counter speciesist prejudices by convincing members of the public to individually reduce their consumption of animal products, especially meat. These organizations use a variety of tactics that depend on the premise that a world with more vegans, vegetarians, and semi-vegetarians is a better world for animals. We examine that premise below as we investigate the net result of removing animal products from a person's diet.

Animals Suffer as a Result of the Typical American Diet

Our society ignores or refuses to acknowledge a great variety of animal suffering, much of it caused directly by human activity. Perhaps the most visible example is the suffering undergone by animals farmed for meat. Most Americans, and even most Americans who self identify as vegetarian, consume meat on a regular basis. As a result, many animals suffer in industrial agriculture and are ultimately killed. To understand the effects of interventions that change individuals’ dietary habits, we need to understand how many animals are killed for food.

The USDA collects fairly exhaustive statistics regarding the largest segments of the animal agriculture industry, and combining these with population information, we can calculate how many land animals are killed each year on a per capita basis. Harish Sethu of Counting Animals has done this, incorporating survey data about the numbers of Americans who follow a vegetarian or meat reduction diet to determine how many animals are affected specifically by the average American diet of eating meat on an (approximately) daily basis. He found that the average American on such a diet consumes about 30 land animals per year, including 28 chickens.

Because the statistics kept regarding aquatic animals are not as detailed as those kept for land animals, and because farmed fish and shellfish are often fed primarily on products derived from wild caught fish, it is more difficult to determine how many fish and shellfish are affected by the typical American’s diet.The USDA keeps some statistics for fish farmed in the United States that are similar to those kept for other farmed animals, but since about 91% of seafood consumed in the United States is produced abroad, these are not as representative to use as the statistics for land animals. Sethu estimates that the typical American eats slightly more than 1 farmed fish per year, but causes the death of about 224 wild fish, either for direct consumption or to feed farmed fish. Similarly, he finds that the typical American eats about 151 shellfish per year, mostly shrimp. Using slightly different methodology and much more conservative numbers for the number of wild caught fish fed to farmed fish, ACE estimates that the typical American eats 2-3 farmed fish per year and in total causes the death of between 46 and 79 fish. Additionally, ACE estimates that the typical American directly consumes about 186 shellfish per year (still mostly shrimp).

Putting this together, a typical American causes the deaths of 262-406 animals per year through their meat consumption. An American who eats eggs affects an additional 2 chickens, and one dairy cow is required for about every 30 Americans.1 For comparison, about 1 animal is killed or used in a lab yearly for every 15 Americans. Even fewer animals are killed for their fur each year: about 1 per every 100 Americans. A larger number of wild animals are killed in the process of crop production, but still only about 0.3 per year for an American following a vegan diet (and thus directly consuming the maximum amount of plant based foods). Overall, meat consumption accounts for a high percentage of the animals directly harmed by human society. Indirect harms due to global warming and habitat destruction may exceed these effects, but industrial animal agriculture also makes significant contributions to environmental changes like these.

The Structure of the Economy Lessens the Role of Individual Choice

The effects of dietary choices on animals are usually invisible in our society. A complex economic apparatus of stores, food processing plants, and farming lies between the typical American and the deaths caused by their food choices. This allows people to perpetuate harm on a grand scale while caring about individual animals that they encounter. It also dampens the effect of individual choices on farmed animals, since one person choosing not to eat meat does not remove any specific animal from the food production system.

Some argue that individual dietary choices have no actual effect on animals. The logic of the argument is that a single person’s decision not to eat meat will be drowned out by random noise even at that person’s local supermarket. One fewer customer in the market for hot dogs will not cause the supermarket to order a different number of hot dogs, so the number of hot dogs produced, and the number of animals harmed in this process, will remain the same.

However, this logic misses the fact that while usually 1 customer will not affect a supermarket’s bulk orders, occasionally the supermarket will happen to be at the point where, with 1 fewer customer in the market for hot dogs, it makes sense to order 1 fewer case of hot dogs. In this case, the customer who has stopped buying hot dogs affects the supermarket’s purchase by a larger amount than simply by the number of hot dogs they might otherwise have bought. Because of this, on average, a person who stops buying meat should expect their local supermarket to reduce its meat orders by the amount of meat that customer previously consumed, or to reduce its prices.

A similar process occurs between the supermarket and its distributor, between the distributor and the food processing plants, and between the food processing plants and the farmers raising the animals. Although the chain is long and very noisy, when an individual stops consuming meat, that shift is felt by the system. Ultimately, fewer animals are farmed for meat.

However, even if the entire system notices a reduced demand for meat products, that does not mean that production falls by the number of products previously consumed by people who are now vegetarian. Fewer people in the market for meat leads to a drop in prices, which causes some other people to buy more meat. The drop in prices does also reduce the amount of meat produced and ultimately consumed, but not by as much as was consumed by people who have left the market.

Economists produce estimates of how much less is produced for each unit that stops being demanded when buyers leave the market for reasons other than price. This is called the cumulative elasticity factor. Their estimates usually depend on collecting data about price, production, and consumption in the real world, and creating an economic model to explain what they have observed. For instance, if a person who normally ate 10 hot dogs per year decided not to eat any and as a result 6 fewer hot dogs were produced, the observed cumulative elasticity factor for hotdogs would be 6/10 or 0.6.

Estimates of elasticity for meat as a whole are not readily available, because economists tend to focus on smaller segments of the industry, for example specifically on beef or on chicken. Even when they are available, they tend to vary widely. For example, ACE uses estimates of the cumulative elasticity factor for chicken that range between 0.06 and 0.7. Our estimates of the cumulative elasticity factor for fish range from 0.15 to 0.62.

Individual Diet Choices Still Have Serious Effects on Animals

Combining the results of the previous sections, we find that if one person chooses to switch from a typical American diet to a vegetarian diet, the results are noticeable for animals.

One person consuming thirty fewer land animals per year results in 1.8 - 21 fewer animals being farmed for meat. Here for simplicity we use the elasticity range for chicken. A calculation that applied a separate elasticity for each species would come up with extremely similar results because chickens are the vast majority of land animals killed each year for food.

One person consuming, directly and indirectly, 232 fewer fish and shellfish per year results in 35 - 144 fewer animals being killed. Here we use ACE’s consumption numbers and, for simplicity, the elasticity range for fish.

Even using conservative estimates, sparing 36 animals is significant. But, of course, we must be careful what we mean by spared. Wild caught fish and seafood are in some sense really spared and can live their lives free of human interference. These lives may still be short and involve considerable suffering, but will necessarily be somewhat longer. Domesticated animals have a different experience. Most of them are brought into existence by humans so that humans can use them for food. In some cases, if the market for that food disappears, the animals will live shorter lives followed by painful deaths, as farmers seek to end their responsibilities for their livestock. In most cases, however, the market does not suddenly disappear all at once. Instead, existing animals will be sold for slightly lower prices than they otherwise would, and somewhat fewer animals will be bred to replace them. Animals who are “spared” will simply not exist at all. Because we cannot experience either nonexistence or existence as chickens in industrial agriculture, there is some room for doubt as to which would be preferable for the individual chicken. However, given the extreme and continuous suffering experienced in modern industrial agriculture, it is plausible that not being born is the better experience.

Most People Do Not Stay Vegetarian Forever

So far, we’ve framed the effects of diet choices as yearly results. However, most vegetarian and vegan outreach is not framed as enrolling individuals to be vegetarians for a year at a time. Instead, usually organizations seek to change minds and diets with a single contact or several contacts repeated over a short period. After that, they hope that people they’ve contacted stay vegetarian or vegan or even become activists for animals, but they don’t usually know what happens or have much influence over it. As such, the interventions are not really producing vegetarian-years (years that a person stays vegetarian), but vegetarian-conversion-events (times that a person decides to become vegetarian). In principle, these might lead to any number of vegetarian-years, and the number might vary by the intervention.

In reality, we have a variety of studies that suggest the average (self-reported) vegetarian stays vegetarian for between 3 and 14 years, and most probably for about 7 years. None of these studies followed a cohort of new vegetarians after an intervention. However, the study from which we got the estimate of 7 years sampled randomly from the population and asked those people who were or had been vegetarian how long their vegetarianism had lasted. It might be that the people involved in the study did not perfectly recall how long they’d been vegetarian. But it’s not likely that they were all vegetarian for an unusually long or short time.

Because the studies did not inquire closely into the reasons people had become vegetarian in the first place, we can’t use them to tell us which interventions have the longest-lasting effects. However, we can be fairly certain that the majority of interventions that create vegetarian-conversion-events result in people staying vegetarian for on average more than 1 year. For each person who declares they have begun abstaining from meat, fish, and shellfish, organizations can expect at least 36 animals to be saved, and probably more like 252. However, they cannot expect that the new vegetarian will go on saving 36 animals per year for the rest of their life.

Some People Would Go Vegetarian Anyway

People adjust their diets regularly for reasons which are not necessarily related to any specific intervention or even to concern for animals. Some groups are especially likely to change their diet because of concerns over health or the environment, or simply because of changes in life circumstances. Particularly when interventions target these groups (as when they deliberately target young women because of their higher base rates of vegetarianism), not all changes attributed to the intervention may really be due to the intervention. Some would have happened anyway.

The best way to compensate for this in our estimates of the effectiveness of an intervention is to use a control group when determining how many people changed their diet because of the intervention. If some people in the control group are eating less meat, the same percentage of people who received the intervention would probably have made similar changes even if the intervention hadn’t happened. If a control group is not available, we must use other sources to estimate the amount of the observed effect that is simply due to background trends and not to the intervention in which we are interested.

Interventions Resulting in Change in Diet Have Other Effects, Too

In many cases, interventions that cause some people to go vegetarian have other effects as well that may be harder to measure. If the arguments given for diet change focus on ideas such as animal rights, they can reasonably be expected to spread discomfort with the use of animals for human gain. Depending on the strength of the message, some people hearing it might be swayed toward some form of activism, from communicating new ideas to their friends and family to joining organizations working to help animals. Since it’s hard to track the spread of ideas and attitudes, interventions that spread both diet change and ideas might have better evidence for their effects on diet, but nonetheless also be useful for spreading ideas.

Individuals who do change their diet may also experience related changes in their ideas and attitudes. Some surveys have found that people who go vegetarian for one primary reason also end up endorsing other arguments for vegetarianism: a health vegetarian might come to be more sympathetic toward arguments about animal welfare, and an animal rights vegetarian might come to believe that vegetarianism has health benefits.2 This, especially for people who have gone vegetarian for reasons not directly related to animals, is corroborated by laboratory studies showing that people attribute less emotional and moral weight to animals when the animals are described as food or when they expect they will soon eat meat.

The attitudinal changes may not be entirely positive, however. If vegetarians feel that they are already working to help animals simply by refusing to eat meat, they may be less likely to take other, more effective, actions. Support for this concern, however, is limited. Some studies in other contexts have suggested that when people have already affirmed their moral identity, they are less likely to take further action. However, others have shown the opposite. The effects appear to be highly dependent on specific contextual factors, and without specific inquiry, it is impossible to know which situation is more true for vegetarians and potential animal activists.


Changing the way people eat is in many cases a highly cost-effective route to helping animals in the short term. However, the direct effects of such interventions are mostly impermanent. Furthermore, although they are easier to measure than the indirect effects, they are not as easy to measure as they may appear upon first consideration. Indirect effects are likely also present, and may be more lasting, but they are much more difficult to measure.


ACE. (2014). Fish number calculations.
ACE. (2014). Vegetarian recidivism.
Sethu, H. (2011-2013). Counting Animals.

  1. Norwood, L.B. & Lusk, J.L. (2011). Compassion, by the pound: The economics of farmed animal welfare. New York, NY: Oxford University Press USA. 

  2. Cooney, N. (2013). Veganomics:The Surprising Science on What Motivates Vegetarians, from the Breakfast Table to the Bedroom. New York, NY: Lantern Books. See especially chapter 7.