The EurekAlert! NASA mission tests ketogenic diet undersea, simulating life on Mars University of South Florida researcher will be in nutritional ketosis during NEEMO 22 mission packs a lot of benefits of ketosis in a small space:

Dr. D'Agostino was selected for his research conducted at the USF Hyperbaric Biomedical Research Laboratory (HBRL) on how extreme environments impact the human body. One of the countermeasures developed is a method to induce and sustain nutritional ketosis with ketone supplement formulations. Nutritional ketosis shifts the body's metabolic state to burn fat rather than glucose as its primary fuel.

The USF-patented method will play a pivotal role in advancing the objectives of the NEEMO 22 mission. Dr. D'Agostino will be in a constant state of nutritional ketosis, which is proven to preserve the genome, protecting DNA. This is beneficial to NASA as it can countermeasure neurological risks that come with space travel such as space radiation, lack of oxygen and stress of small spaces. (emphasis added)

So while it may be possible for one to achieve ketosis with a modified diet, in the NEEMO 22 experiment the subject will receive a ketone supplement.

Might a low-carb diet on Mars make us more resistant to radiation, better able withstand lack of oxygen, and be more comfortable in small spaces? Will there be ketone-laced chocolates to enhance compliance?

Question: The short EurekAlert! may have just mixed a few different points together in the two highlighted sentences. Has NASA or any other space agency looked into ketosis as a potentially beneficial state in some situations? Is it possible a low-carb diet might be recommended for extended spaceflight missions?

update: Recent related news:

I don't really understand what ketosis is but I can copy/paste from Wikipedia

Ketosis is a metabolic state in which some of the body's energy supply comes from ketone bodies in the blood, in contrast to a state of glycolysis in which blood glucose provides most of the energy.

[...]Longer-term ketosis may result from fasting or staying on a low-carbohydrate diet (ketogenic diet), and deliberately induced ketosis serves as a medical intervention for various conditions...

A bit more information about human metabolism and ketosis can be found in this excellent answer. Here is a reposted graphic from there:

enter image description here

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    $\begingroup$ The linked article rang multiple junk science alarms for me. E.g., this doesn't seem very science-literate: "the microgravity (or harsh) environment they will experience in space." Ketogenic diets are just one of the latest food fads. Back in the 1980s, the fad was that carbs were supposed to be good, the base of the food pyramid. Now the fad is that you're supposed to avoid carbs. If you don't eat enough carbs, you go into ketosis. The claims about ketosis and DNA sound silly, and what does ionizing radiation have to do with going to the bottom of the ocean? $\endgroup$
    – user687
    Commented Jun 12, 2017 at 4:18
  • $\begingroup$ @BenCrowell thanks for your opinion but I'm pretty sure this is not junk science or I would not have asked here. The problem may be that the paragraph was shortened at the last minute by an editor, and a few separate items were compressed together. Have you done any research/reading on this study (NEEMO 22), or are you just speaking from the gut? (pun intended, it's a dietary-related study ;) $\endgroup$
    – uhoh
    Commented Jun 12, 2017 at 4:28
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    $\begingroup$ @BenCrowell The same basic text is on the USF site. Doesn't mean that it's not bad science (or more likely, bad reporting of the science), but it does mean that we may need to investigate this one further. $\endgroup$
    – called2voyage
    Commented Jun 12, 2017 at 18:17
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    $\begingroup$ @uhoh: I wonder what solid research is there into influence of ketosis on health and performance. I recall an account of a person experimenting with ketosis, reporting severely compromised mental capacity ("It makes you dumb. 'Forget your pants to work' level dumb", if I recall the quote correctly.) $\endgroup$
    – SF.
    Commented Dec 26, 2017 at 2:50
  • $\begingroup$ @SF. then type "influence of ketosis on health and performance" into scholar.google.com and find out what solid research is there. I don't want to have a conversation about it in comments here. Let's focus on answering the question. $\endgroup$
    – uhoh
    Commented Dec 26, 2017 at 3:14

3 Answers 3


To summarize what ketosis is, as shown in the nice summary graph you included, there is 3 main types of nutrients we can use: carbohydrates, fats and proteins.

Carbohydrates can be broken down and converted into glucose (well, not all, such as many of the components dietary fiber, since we lack the enzymes to break these down. This is why if we eat wood, which contains a lot of cellulose, we do not actually get any nutrients from it). For long-term storage, we can use glucose to generate a polymer known as glycogen, which is stored in the liver (but not in other organs, such as in the brain).

Fats are broken down mainly into fatty acids, which can be broken down further into a molecule called acetyl-CoA, which can be used to obtain energy (in fact, when obtaining energy from glucose, we also need to go through the intermediate step of conversion to acetyl-CoA). For long-term storage, fatty acids are merged with glycerol to form triglycerides, which are the main form of storage in fat cells. This is in fact how we store most of the excess energy coming from the nutrients we consume, and it is the main constituent of "body fat".

For this discussion, I think we can leave proteins as a source of energy out (at least for the time being), since they cannot be used as the main source of energy over a long period of time (we would need to consume very large amounts of protein to cover energy needs just from protein, and that would lead to kidney and liver damage). The main purpose of eating proteins is to break down into amino-acids, which we then use to produce our own proteins (basically, almost every functional thing inside our cells is a protein).

Our brain cannot use fatty acids as a source of energy, because fatty acids are delivered to the organs for use as an energy source bound to a large molecule (a protein) called albumin. The reason is that they need to be delivered through blood, but fatty acids are not soluble in aqueous solutions (which blood, and the intracellular medium, are). Albumin, however, is soluble in aqueous solutions, so by binding fatty acids to it, we can force them to be soluble. If not, the fatty acids would just clump together, like when we try to dissolve oil in water.

Why does this matter? Well, our brain is a special organ (!), and therefore it has much more protection layers than other organs. For example, the so-called blood-brain barrier. This is basically a physical layer formed by a specific type of cells that tightly controls (much more tightly than what happens for other organs) what goes from the blood stream into the brain. This is essential for our survival: for example, it helps to keep pathogenic microorganisms away from the brain. But it also creates problems, since it also means many molecules (specially large molecules) that can reach other organs, cannot reach the brain (in fact, it is one of the main consideration that needs to be taken into account when designing medicines that are targeted to the brain). Amongst these is albumin, but not glucose.

So what happens under normal circumstances, is that our brain is fueled by the glucose in food we eat. If we have not eaten in a while, our liver breaks down the stored glycogen (the polymer of glucose), the resulting glucose passes to the bloodstream, and then goes to the brain. By doing so, we don't need to be constantly eating things that have glucose to keep our brain working.

However, the amounts of glycogen we can store are limited, and they will run out in a few hours (shorter time if you do intense exercise). We usually don't black out even if not eating in a few days, so what's going on here? You might think maybe we are making glucose from the large stores of triglycerides that we have in our body fat. But humans cannot make glucose from triglycerides, fatty acids, or any derived molecule (plants, for example, can do so). Instead, what we can do is to produce the so-called ketone bodies from acetyl-CoA (which can be readily derived from fatty acids). Ketone bodies are in fact a range of several molecules, the main ones being acetone (yes, the same as the organic solvent!), acetoacetate and 3-hydroxybutyrate. These molecules are not the most efficient way to store energy, but they have an advantage, which is that they can readily go into the blood stream and cross the blood-brain barrier. So they can be used by the brain as a source of energy, and this is how our brain survives in the long-term if we do not consume any food.

This process of producing these ketone bodies (I do not really like the name by the way, because it makes it sound like some sort of big-sized inclusions, while they are just small molecules, but the name is widely accepted and used) is what is called ketosis. You might have read that ketosis is good for weight-loss, and the reason is that if our body starts to produce at large scale these ketone bodies, it is doing so at the expense of body fat.

However, it comes with consequences. Nutrition websites frequently called this "the keto flu", because some of the symptoms are similar to those of flu. These include headaches, increased irritability or change of mood, digestive tract disorders, dizziness, amongst other. It is true these can go away to some extent, but the extent of the symptoms, how much and when they disappear varies. There is in fact quite a lot of research about the long-term effects of ketosis still going on, with some suggesting even an increased risk of cardiovascular disease.

I have not been able to found (on a quick search) a paper directly analyzing if ketosis can make normal cells be more resistant to ionizing radiation, but there seems to be quite a bit of research on the combined effects of ketosis and radiotherapy on cancer cells. See for example this, this and this recent review. These papers seem to suggest that the sensitivity of cancer cells to radiation therapy is in fact increased by ketosis. The reasons seem to be unclear, and might be partially related to an effect of ketosis on the production/elimination of the so-called reactive oxygen species (ROS). ROS are unstable molecules derived from molecular oxygen that are a full different subject on its own, but in short they are involved in aging, inflammatory processes, mutations in the genetic material that lead to cancer, and many other "bad" processes. So does ketogenesis promote or reduce the generation of such ROS? From my understanding, it is unclear. For example, quoting from the mentioned review, paper:

Finally, the antitumor effect of the KD has been associated with both increased and reduced ROS levels, indicating that the KD potentially interferes with the tumorigenic ROS balance of cancer cells

Where KD means ketogenic diet. So basically it is not known! Maybe the increased sensitivity of cancer cells to radiotherapy is just a combination of the radiotherapy itself and the negative effects of ketosis on cancer cells, and not necessarily a sign that it makes cancer cells more sensitive to radiation... In any case, I have not found any strong evidence to suggest that ketosis makes cells more sensitive or more resistant to radiation.

A diet that induces ketosis (i.e., one where foods with carbohydrates are eliminated to a very large extent) also needs to be very carefully planned, specially if aimed to be sustained in the long term, since we also need vitamins and other micronutrients (nutrients that we need in very small amounts, not for energy production, but in other for components of our cells to be functional). By strictly eliminating foods with carbohydrates (including fruits) from the diet, we might be also removing sources of said micronutrients. Of course, I'm sure if a ketogenic diet was going to be implemented by any space agency, this would certainly be taken into consideration, but I thought it was worth mentioning that this also needs to be kept in mind, since it might mean that a very strict ketogenic diet is difficult to sustain in the long term.

So given the lack of evidence to support an increased resistance to radiation, the presence of quite negative side-effects and the fact that the diet might lead to micronutrient deficiencies if kept very strictly ketogenic, I do not think it sounds like a very likely choice for people potentially living on Mars. Especially given that this would be over a relatively long period of time. And particularly, with consideration to the ability to withstand small spaces, given that ketosis can lead to irritability and mood changes, it might even be the opposite. Another side effect is that when ketosis happens, we exhale the ketone bodies molecules through our breath (including acetone). On Earth, this does not matter much, since it just dissipates onto the atmosphere. But in closed spaces, having increasingly large concentrations of acetone and acid molecules in the air, might be something to worry. It would certainly require consideration. As a side note, I recently saw a product being advertised as a hand-held, portable device able to enable you to hack your metabolism by simply analyzing your breath; I'm quite sure this is to a large extent simply analyzing the concentration of acetone or other related molecules on the air we exhale.

It doesn't seem to be a good idea...

I have also found this (quite long) report by NASA about the particularities of nutrition in space exploration. Ketosis is briefly mentioned in pages 12 and 14, and it does not look like they thought of it as a great idea. Quoting from page 12:

The metabolic condition of ketosis, which would be expected to result from starvation, not only would have metabolic effects (including decreased appetite), but might also affect other aspects of the mission (for example, the life-support systems might not be able to remove the ketones from the air). Ketoacidosis can obviously have negative effects on acid-base balance, which in turn can affect bone, muscle, and other systems.

And from page 14:

A ketotic state would likely impair performance of crewmembers, as seen in studies conducted by the military (71), as well as increase renal stone risk secondary to reduced urinary pH (87-89). Other aspects of the mission would also be at risk (for example, the life-support systems may not be able to remove exhaled ketones from the air). Toxicity of carbohydrate has not been well studied, and would likely be an issue only because it would displace other nutrients (protein and fat) from the diet.

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    $\begingroup$ Thank you for this thorough, thoughtful and well-sourced answer! $\endgroup$
    – uhoh
    Commented Dec 23, 2021 at 3:34
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    $\begingroup$ Glad that you found it of interest! And thanks for highlighting the main point. I forgot to put that clearly after the (probably too) long previous considerations! $\endgroup$
    – Rafa
    Commented Dec 23, 2021 at 3:37
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    $\begingroup$ a common result of writing thoroughly and thoughtfully :-) $\endgroup$
    – uhoh
    Commented Dec 23, 2021 at 3:54

Can ketosis increase radiation tolerance?

Probably Not.

It's certainly something worth studying - science is all about looking into harebrained ideas! But I don't expect this one to pan out.

Background: I was the Chemistry and Radiological Controls Officer on a nuclear submarine.

Types of Damage

There are two broad categories of radiation damage we care about: DNA damage, and cell damage. Roughly, DNA damage means cancer, and cell damage means radiation poisoning.

In one case, and ion interacts with the DNA of a cell, and in the other the ion interacts with some other part of the cell - an organelle, the cell wall, etc. In both cases, the cell potentially has a chance to repair itself.

Repair Mechanisms

The cell runs a kind of checksum on its DNA to identify changes, and attempts to correct them. A completely separate process (that frankly I know nothing about) allows the cell to identify defective operations in organelles and attempt to correct them.


Scientists have determined that inflammation is negatively correlated with the efficiency of the DNA repair mechanism - higher inflammation means the checksum works less well. I don't believe the causal mechanism is well understood. (This is why you hear people talk about anti-oxidants: they are correlated with lower inflammation.)

Ketosis' Effect

Ketosis appears to reduce inflammation, which should theoretically improve the efficiency of the cells DNA checksum process. So the whole question of "will this increase radiation tolerance?" isn't absurd on the face of it.

Magnitude and Poisoning

The two main problems I see here are:

  1. What's the magnitude of the effect?
  2. What about radiation poisoning?

Generally, eating a healthy diet and exercising leads to lower inflammation. Yet people with healthy behaviors still get cancer. Obviously, the DNA checksum procedure is fundamentally imperfect. I'm highly skeptical that some specific diet will improve that checksum performance by any significant amount over what you could get out of a normal, healthy lifestyle.

Even if the chucksum was perfect, that would not protect against cell damage to non-DNA portions of the cell. Someone with a perfect checksum would be immune to cancer, but would still die a painful death after a large dose of radiation. ("fun" fact - your digestive track is highly susceptible to radiation poisoning, which will likely impact your ability to maintain ketosis!)

Nerve cells never divide after childhood, so lengthy exposure to elevated radiation will probably lead to a mental decline, even if cancer is completely out of the equation.


If we have the shield our astronauts from radiation to protect them from digestive track collapse and severe mental decline, we will probably just use shielding to protect them from cancer as well.

But again, I'm all for doing the science, determining the magnitude of the effect, and seeing if that allows us to maybe cut back the weight of shielding just a little bit...

But I'm not holding my breath.


Bad idea.

Ketosis results in muscle atrophy (wasting).

Glucose is the primary fuel of the heart and brain. No blood glucose = death. Ketones are not an adequate substitute for glucose.

Normally, the body breaks down dietary carbohydrates to provide glucose. Extra glucose is stored as fat, but fat cannot be turned back into glucose.

In severe carbohydrate restricted diets, the body uses available resources to manufacture glucose in a process called gluconeogenesis. This requires protein https://en.wikipedia.org/wiki/Gluconeogenesis . The only bulk source of proteins available to a starving body is muscle.

A strict ketotic diet caused significant, rapid muscle loss. This Nature paper showed 16-28% muscle mass loss in 1 week. https://www.nature.com/articles/s41598-019-56166-8 .

Those grocery store checkout diets which promise "Loose 14 pounds in 14 days" are right: 7 pounds of muscle and 7 pound of water.

Microgravity already causes muscle atrophy. Adding a ketogenic diet would compound the problem.

Adding protein to make up for the loss of dietary carbs would help with the muscle atrophy, but would be an added load on the kidneys which are already challenged by the calcium load from microgravity bone loss.

The Hippocratic oath says," above all else, do no harm". Unless there is evidence (not rationalization) of net benefit, putting Mars explorers on Keto diets would be uncontrolled and unethical human experimentation.


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