Could Human Photosynthesis Be Possible?

Photosynthesis—the process by which plants turn sunlight into food—may be for many people a reminder of high school science class and nothing more. But a growing number of scientists, tech entrepreneurs, and health gurus are considering whether it may be possible for human beings to somehow replicate or at least approximate the way that plants gather nutrients to sustain and grow themselves.

The increased interest in so-called “human photosynthesis” in the last several years is often considered to be a part of a larger movement known as transhumanism. Transhumanists believe that human beings may be able to use technology to “biohack,” that is, to modify and enhance themselves both physically and cognitively, using tools to be able to outperform the human body in its natural state and even to live longer or to prevent death entirely.

Transhumanists supporting the idea of human photosynthesis point to the way that plants receive nutrients—by using energy from sunlight to oxidize water and turn carbon dioxide into glucose—as far more efficient in many ways compared with the human method of receiving nutrients. Humans must hunt or search for (or, worse, spend time and resources planting, nurturing, and growing) food, then cook, chew, and digest that food in order to finally assimilate its resources. If humans could somehow find a way to replicate the photosynthesis process plants display, the thinking goes, there would be a host of benefits for individuals and for the planet.

Below, we take a closer look at what human photosynthesis might look like, the likelihood that this is a possibility in our future, and the potential benefits it could provide.

Human Photosynthesis: Synthetic Biology

For some believers in the possibility of human photosynthesis, the key to achieving this goal is in the emerging field of synthetic biology. Synthetic biologists aim to utilize genetic material from different sources to produce new organisms, or to enable existing organisms to perform new functions.

On the one hand, this seems to be an outlandish idea in the case of humans and photosynthesis, as it might require somehow combining elements of human and plant DNA. Humans and plants share common genetic ancestors, but one has to look back hundreds of millions of years to find them. Since that time, we have diverged from plants in countless ways. Perhaps most significantly, plants have generally become thinner and more transparent over the course of their development, while humans and most other animals have grown thicker and more opaque. The latter two of these traits are not conducive to photosynthesis for a number of reasons, not the least of which is that large animals now require a massive amount of energy in order to even just maintain the status quo.

But, synthetic biologists may argue, there are aspects of human and plant cells—and human and plant genetics—that may be more similar than you would expect, and which could make the idea of integrating elements of both forms of life less far-fetched than it would appear.

A key bit of evidence supporting the possibility of human photosynthesis is the fact that there are already some animals that photosynthesize. For example, the pea aphid is a type of insect that makes use of pigments to harvest sunlight and transfer it to cells in order to produce energy. Elysia chlorotica is a type of sea slug that achieves something like photosynthesis in a different way: it acquires chloroplasts, the cellular parts of plants producing chlorophyll in order to make photosynthesis possible, by eating particular algae. Scientists have observed these slugs surviving without food for nine months, subsisting only on energy from sunlight. Colonies of coral make use of photosynthetic dinoflagellates to harvest energy from sunlight, while spotted salamanders use algae to harness solar power in developing within their eggs. But some scientists believe the sea slugs in particular may offer a path toward human photosynthesis.

Elysia chlorotica eat algal chloroplasts and install them within their digestive tracts, exchanging certain genetic elements along the way to help the slugs to maintain the chloroplasts over time. This seemingly minor swapping of DNA could be what helps the slugs to continue to be able to gain energy from sunlight over many months at a time.

By this token, if humans could somehow embed chloroplasts within their own skin, and similarly make use of algal DNA to help to rebuild and maintain those chloroplasts, it’s possible that we could begin to perform a similar function as the sea slugs, taking sunlight and using borrowed chloroplasts to convert it into energy.

Barriers to Human Photosynthesis

Of course, tiny insects and sea slugs have significantly less mass to maintain compared with humans, and similarly use only a small fraction of the energy a human does in order to perform basic bodily functions, among other things.

The amount of skin surface area that would be required in order to photosynthesize enough energy to replace even one regular meal would be immense. This points back to the different structures that plants and humans have evolved over millions and millions of years. Plants use wide, thin leaves to maximize surface area while minimizing total volume, an ideal combination for efficient photosynthesis. Humans, on the other hand, are thick and fleshy. We have much higher volume-to-surface-area ratios, making it that much harder to even potentially gain enough energy from photosynthesis to survive (should that process actually be possible someday).

Beyond the simple issue of surface area, there are the logistics of getting sunlight to the chloroplasts in the first place. Humans would have to be largely motionless and see-through in order for this to work, and there would have to be at least thousands of algae per skin cell even on top of those other considerations.

Possible Benefits of Human Photosynthesis

All of these signs point to the unlikelihood that humans will be fully subsisting off of a process resembling photosynthesis any time soon, if ever. However, there is a potential middle ground: what if it’s possible to make use of the powers of photosynthesis to help supplement normal human diets? The animals that make use of photosynthesis or similar processes generally do so in this fashion, not in order to fully sustain themselves using sunlight alone. Instead, they make use of photosynthesis to provide emergency or back-up nutrients at a time when regular food sources may be unavailable.

Human photosynthesis, if we ever achieve it, could do more than just give us protection against starvation. If this process could be harnessed for medical purposes, for instance, it’s conceivable that humans could use photosynthesis to help to aid in injury or wound recovery, or to aid ourselves in achieving a small boost of energy for athletic purposes, say.

In June of 2023, a study in the academic journal Nature Communications found that human photosynthesis could play a significant role in our ability to sustain ourselves while living off of planet Earth. With more and more talk about returning humans to the moon and even attempting to bring people to Mars, the question of long-term sustainability and nutrition is a major hurdle. A photoelectrochemical (PEC) device could be used to replicate photosynthesis in these scenarios, turning water into oxygen and recycling chemicals like carbon dioxide in the process. While humans would not be photosynthesizing through algal components in their own cells in this case, we would nonetheless be capitalizing on the plant process to help to provide essential components of life outside of Earth’s atmosphere and ecosystem.

As distant as some of these goals may seem, there are tremendous incentives to try to make human photosynthesis possible. By helping to alleviate the need for traditional food sources even partially, photosynthesis would be a powerful tool to stave off hunger for a rapidly growing population that, by 2050 could require as much as 56% more food globally as compared with needs in 2010. Besides helping to fight global hunger, photosynthesis could be a powerful tool in the battle against climate change, allowing humans to focus precious planet surface space to growing plants not for food but with the goal of alleviating the underlying causes of climate change.

Human photosynthesis may still be far off, but recent developments are encouraging. Just last year, chemists at the University of Chicago developed a new artificial photosynthesis mechanism 10 times more efficient than previously existing tools, for example.

Cheat Sheet

Human photosynthesis, the belief that humans may someday be able to benefit from sunlight by turning it into energy in the same manner as plants, is broadly connected to a larger movement known as transhumanism.
Transhumanism holds that human beings should make use of developments in science and technology to create, use, and integrate into their own bodies tools to aid in physical and mental performance or longevity.
The process of photosynthesis for plants involves utilizing energy from sunlight to oxidize water and turn carbon dioxide into glucose.
If human photosynthesis is someday possible, it could partially or significantly reduce the need for traditional food sources like crops, help to eradicate global hunger, and yield benefits to the environment, among many other things. Some estimates suggest that by the year 2050 humanity will require 56% more food globally as compared with 2010.
Some believe that the key to potential human photosynthesis lies in synthetic biology, a field that makes use of genetic information from one living organism in another in an attempt to improve physical processes and performance.
Supporters of the movement to develop human photosynthesis may cite a number of small animals that either photosynthesize or complete a similar process, including sea slugs and pea aphids.
Elysia chlorotica, a type of sea slug, eats algae and integrates the chloroplasts within into its own digestive system. It is able to sustain those chloroplasts for an extended period of time and can harness them to photosynthesize sunlight. Some of these slugs have been observed going without food for up to 9 months at a time.
Major hurdles to the human photosynthesis project include the fact that humans are significantly larger than sea slugs and other animals known to replicate this process, that our energy needs are far greater, and that we have opaque skin, among many others.
Still, some believe that photosynthetic tools like a photoelectrochemical (PEC) device could be used to mimic photosynthesis in limited capacities—say, to supplement regular nutrients consumed through a food diet, or to help to aid in wound recovery.
Finally, scientists are pursuing the possibility of human-controlled photosynthesis as a way to potentially sustain life on Mars or in other space missions into the future.