In this guide, we will look at which foods to feed with caution and which are best avoided altogether. We’ll reveal the dietary trends that are bad for your rats and why, before looking at antinutrients – those naturally occurring substances in plants that can spell trouble for your rats.
A Forbidden Foods List With a Difference!
So, you might be thinking that there are already lots of lists around that tell you what foods rats can’t eat – do you really need another? The trouble with a lot of what is already online is that it is mostly copied in one way or another from one original list, and sadly that list wasn’t very accurate.
We have independently researched every food on the list repeatedly over the past couple of decades as information and understanding has grown about topics like phytochemicals, antinutrients, and toxins. And we’ve looked at them again for this article to give you the latest information available.
AVOID These 4 Dietary Trends & You Are Halfway There
Feeding Too Much Fat to Your Rats
It is well established (by laboratory research) that excessive fat in a rat’s diet (even healthy fats) can lead to rapid growth in young rats (excess calories), obesity in adult rats (excess calories), mammary tumors (the fat content itself) as rats age and decreased longevity.
It’s often not the fat itself that’s the problem but the overall calories that increase with the inclusion of higher levels of fat in a high carbohydrate diet. Interestingly, high fat calorie-restricted diets do not share all of these effects.
So, in the context of a standard carbohydrate-based pet rat diet, how much is too much?
In a table produced by the National Research Council, which lists the nutrient requirements for laboratory rats, fat requirements are listed as 5g per 100g of diet – or 5% – across all life stages.
Fat is one of the nutrients that is unaffected by antinutrients like fiber and phytochemicals. Therefore, most of the fat that is available in food can be absorbed into the body. So, a rat’s diet should be roughly 5% fat.
Pet rats eat on average 15-20g of dry food per day. This enables us to work out how much fat they need per day:
- 5% of 15g is 0.75g
- 5% of 20g is 1g.
So, most rats need between 0.75g and 1g of fat per day – which is a tiny amount that is easy to get from a mixed grain and seed diet.
Feeding much more than this on a regular basis can lead to rapid growth, obesity, mammary tumors, and premature death, due to the increased calorie load and its effects.
Therefore, it is important not to feed too many high fat treats as they can soon impact the overall fat levels in the diet. And it’s probably wise to exclude all high fat, low nutrient foods like fries, chips, and (non-fish) animal fats.
Some high-fat foods like hemp, flax, sesame, pumpkin seeds; nuts, coconut, avocado, and oily fish are excellent for rats in terms of both healthy fats and micronutrients. They should be included as the main fat portion of the daily diet.
Feeding Too Much Sugar to Your Rats
Regular sugar in the diet has several major impacts on health and well-being including, tooth decay.
This could affect the rat’s molars which are not renewed throughout life. Other issues include metabolic disorders, deranged immune system function (including changes in gut flora and increased aggression from activation of the neuroimmune system), and obesity.
- Fruit does contain sugar (fructose), but it should be included in the diet in small amounts for its excellent health benefits. Berries are particularly good for rats as they are low sugar and high in antioxidants and vitamins.
- Sweet pastries, cakes (other than those sweetened only by fruit), and milk or white chocolate are among the foods that are best avoided altogether or kept for a once a year occasion like a birthday.
- Simple carbohydrates (processed ‘white’ carbohydrates) and potatoes are foods that can readily be digested into glucose (sugar) molecules and should not make up the bulk of a rat’s diet unless the rat is sick and struggling to maintain weight.
A diet that is mostly complex carbohydrates is best for the bulk of a rat’s life, with a few processed carbohydrates added to provide readily accessible energy. The ratio of processed carbohydrates can be increased as a rat ages as this will increase the absorption of micronutrients and energy.
Feeding Your Rats ‘Ad Lib’ – The Problem of Overfeeding
There is a vast amount of research involving rats and the subject of dietary restrictions and fasting periods. Adlib feeding is leaving food in your rat’s cage all the time, to nibble on whenever they please, and it has been shown to shorten the rat’s lifespan considerably.
Adlib feeding meets the brain and the body’s energy needs from glucose, and it results in a series of frequent peaks and troughs in blood sugar. Fast periods (which would be a natural part of a foragers eating pattern) cause the body to burn fat for energy.
During fat burning the energy needs are met by ketones rather than glucose, which seems to provide several benefits. These include protection against chronic disease, improved brain function, and increased longevity.
Intermittent fasting can also help to manage weight in rats who can be prone to obesity, and you don’t have to try very hard to fast your rats, because of their rapid metabolism.
One easy option is to feed their daily portion of food (try 20g per rat as a generous portion) once in 24 hours in the evening – the beginning of their most active 12-hour period. Then three (not consecutive) days a week just feed half rations (10g per rat).
This would look something like:
- Monday: 7 to 10g/rat
- Tuesday: 16 to 20g/rat
- Wednesday: 7 to 10g/rat
- Thursday: 16 to 20g/rat
- Friday: 7 to 10g/rat
- Saturday:: 16 to 20g/rat
- Sunday: 16 to 20g/rat
You would also need to avoid carb-based treats on the lean days and just feed low carb vegetables if you wanted to give something extra.
The positive effects of intermittent fasting are not insignificant, with some studies showing up to 80% greater longevity! It’s important to note that the rats are still getting a similar quantity of food overall. This isn’t a calorie restricted diet.
Intermittent fasting is not about restricting the amount of food – just about having fast periods in between eating. The lesser amount of food given on the lean days simply means that it is eaten at the beginning of the 24-hour period so that a lean period will follow.
Feeding High Protein and Phosphorus Diets As Rats Age
Laboratory studies have shown that rats as a species experience a slow decline in kidney health throughout their lives, with chronic kidney disease usually tipping towards end-stage renal failure around 30 months.
Knowing this means that you can alter your rat’s diet as they age to help protect the kidneys and slow this decline.
Diets that are high in all three will have the greatest effect in increasing the rate at which the kidneys decline. For this reason, lowering the protein and phosphorus in a rat’s diet as they get older has a protective effect. As does not overfeeding (calories) throughout life.
- Protein for rats over 18 months should generally be no more than 12% of the diet, which is very easy to achieve just by selecting an appropriate food or mix.
- Phosphorus is a bit harder to reduce in the diet as it’s in all grains and often at levels in excess of what a rat needs.
Select a diet based on lower phosphorus grains like rice, corn, millet, sorghum, and barley to help support your rats as they get older. Processing grain also reduces phosphorus, so this is the time to add more processed grains as well.
Antinutrients – What Are They and Why They Matter
As well as nutrients, food also contains antinutrients; compounds and chemicals that interfere with the absorption of the nutrients or create other ill effects.
There are many different types of antinutrients and some – like fiber – have both positive and negative effects.
We all know that fiber is essential for a healthy gut. But do we also realize that fiber can prevent up to 50% of the minerals and protein in food from being used by the body?
This shouldn’t stop us from feeding our rats fiber but rather inform us to feed enough nutrients to make up the deficit.
All fruit, vegetables, grains, nuts, and seeds contain some antinutrients because at the very least they contain fiber. Other common antinutrients include:
Found in the bran layer of all whole grains. Phytates will bind with minerals and prevent their absorption in the gut.
Such as lectin – the best known of these is the form of lectin (lectin phytohemagglutinin) that is in raw legumes like kidney beans, which can be lethal as is causes red blood cells to clump together. Thankfully it is a protein that is denatured by vigorous boiling leaving the beans safe to eat.
Amines, nitrates and nitrosamines
Nitrates and/or amines are found widely in fruit, vegetables, and even oily fish. They can combine in the gut to create nitrosamines that are thought to be carcinogenic.
However, it is also thought that the antioxidants in vegetables and fruit protect against this effect and more than cancel it out. I’ve only included them as antinutrients as they often come up on forbidden food lists.
Oxalates (oxalic acid)
A naturally occurring plant acid that – in excess – makes plants poisonous. During digestion the oxalates can bind with minerals (like calcium and iron), reducing the amount available to the rat’s body and creating tiny insoluble crystals.
The body also makes oxalate crystals itself. They are passed out in feces or urine. In excess, these can cause kidney stones (a condition rats don’t seem to suffer from). Indeed, even when trying – in a laboratory setting – it is extremely difficult to induce kidney stones in rats.
Foods that are high in oxalic acid include cocoa, nuts, beans, seeds, greens (especially spinach and beets) and sweet potato, amongst many others. You will see that these foods are still considered healthy and are not a problem for most people (or rats!) to eat regularly.
The exception might be if your rat is already diagnosed with kidney problems since oxalate crystals are excreted by the kidney. Even so, these foods don’t need to be excluded, just fed in moderation.
Naturally occurring ‘pesticides’ that some vegetables contain in order to deter pests and diseases. They give the plant a bitter taste. Glucosinolates are found in cruciferous vegetables, such as broccoli, cabbage, cauliflower, and sprouts.
They are known to have a protective effect against cancer and are generally considered healthy, but in excess, they cause thyroid issues and may affect reproduction. In this instance, “excess” is defined as being the primary food source and would never apply to rats.
Small organic molecules that act on the nervous system with various effects. Examples of plants that contain alkaloids are tobacco, coffee, cannabis, belladonna, and cinchona.
One toxic alkaloid is solanine which is found in potatoes where the skin has gone green. These should never be fed to rats.
A few plants contain oestrogenic compounds in notable amounts. Examples are soy, flax, oats, barley and sesame seed. These compounds have been shown to produce feminization of male rats when given in a concentrated form. No such effect is noted when rats are fed on mixed diets containing these foods.
Unnecessary Additives That Can Affect Your Rats
Table salt is made up of sodium and chloride, both of which are needed by the rat in small amounts.
There is no need to add salt to your rat’s diet as enough is available naturally in their food to meet their needs.
Rats are tolerant of some extra sodium and it is fine to feed a little food to which salt has been added – just don’t add it as routine if you are cooking for them. Rats sweat very little, only through the soles of their feet. So they don’t lose salt in hot weather and don’t need ‘salt licks’ or mineral blocks containing sodium.
Many pet foods are now preserved with vitamin E, but some that contain poultry fat or other animal fat as a separate ingredient will still contain artificial preservatives, such as, BHT, BHA, and ethoxyquin.
These are known carcinogens (in larger amounts). BHT causes liver tumors in rats and ethoxyquin’s primary toxic effect on the kidneys. Since the kidneys are a vulnerable organ in the rat, this should be a concern, especially as this preservative increased the rate of kidney degeneration in rats in laboratory studies.
Labeling like “No added artificial preservatives” (rather than “No artificial preservatives”) is likely to suggest the presence of at least one of these preservatives, as manufacturers don’t have to list additives that are added to ingredients at source. “USA or EC permitted antioxidants” is another euphemism for artificial preservatives.
These are often used in pet food to make it look more appealing to human eyes. The most common artificial colors used are:
- Yellows 102, 104, 107, 110
- Red 122 through to 129
- Blues 131, 132, 133
- Green 142
- Black 151, 153
- Browns 154, 155
The main problem with artificial colors is sensitivity. Some individual rats may be more sensitive to the unwanted effects of them, which include problems with the skin, gut, respiratory tract and the central nervous system.
While artificial colors may not cause your rats any issues, they are completely unnecessary and, as such, are best avoided to ensure zero negative effects.
Foods That Often Appear on Forbidden Food Lists (Without Good Reason)
The molds used to make blue cheese are not toxic to rats, and I got this straight from the mouth of a microbiologist who is also an extremely experienced rat keeper. You may not want to feed blue cheese because of the fat content, but the molds are edible and are not capable of producing mycotoxins and aflatoxins, which are the ones that make animals ill.
Spinach/ Rhubarb/ Beets
These specific foods are often included on lists, despite being only some of the foods that contain higher levels of oxalates. Oxalates in foods are not a problem to rats at normal dietary amounts. See section above – Oxalates.
It is often said that green bananas contain an enzyme that inhibits starch digestion. Unripe (green) yellow Cavendish bananas actually contain amylase, which is an enzyme that digests starch! It should be noted that in other cultures “green bananas” can refer to other varieties of banana that are used in savory dishes. Unripe yellow bananas are safe for rats.
Raw Sprouts, Cabbage, etc.
These foods that are often (wrongly) included on forbidden food lists for rats as not suitable to feed raw. Some of the polyphenols in sprouts and cabbage reduce the absorption of thiamine (vitamin B1) in the gut.
The effect of these antinutrients is greatly reduced by the presence of ascorbic acid, tartaric acid, and citric acid, all of which occur naturally in fruit and vegetables. Sprouts have good amounts of citric acid, minimizing this effect.
Just like us, our rats can eat these foods regularly without suffering from a B1 deficiency. Interestingly, cooking has no effect on the polyphenols, so raw – or cooked – are fine.
Raw Sweet Potato
Raw sweet potato is often included on forbidden food lists for rats because they contain tiny amounts of cyanogenic glycosides (CGs).
CGs convert to cyanide when eaten, but the amounts in sweet potato are nowhere near toxic levels. Many other foods contain CGs yet are never mentioned. You can safely eat or feed sweet potato raw, but we would suggest baking it because it tastes much nicer!
Corn is often included as it is a source of toxic mold. However, to suggest that this is the case for corn that is prepared for animal consumption by reputable companies is simply untrue.
While not usually on forbidden food lists, some people think they can’t offer fermented vegetables like kimchi, sauerkraut, and pickled fermented cucumbers to their rats. These vegetables are excellent for supporting gut health and can certainly be offered to rats – who may, or may not, accept them.
Some Groups of Foods to Feed With Caution
Thick, Sticky or Doughy Textured Food
Rats have an extra flap over the entrance to their stomach from the esophagus (gullet) that stops them vomiting or regurgitating food. Because of this and their dentition, which is designed to grind food, they can be prone to pseudo-choking on foods like mashed potato and peanut butter.
Very occasionally, people have noted similar problems with bread, although many people feed wholegrain bread, granary bread or a whole uncut wheat loaf to their rats on occasion, without any issue. Our own experience is that bread tends to be shredded down into crumb and doesn’t cause problems.
A rat who is gagging on stuck food is rarely actually choking (they can still breath and the trachea/windpipe isn’t blocked), they will gag and salivate to try to clear food that has stuck on its way down.
Sometimes they clear the food down into their stomach and often they clear it back up into their mouth and then spit it out (not vomiting as it’s never reached their stomach). Very occasionally a rat will actually choke and stop breathing as the trachea gets blocked off.
Nut butter can be let down a little with water or plant milk or just spread really thinly on a slice of cucumber or other vegetables. We often feed rolled granary bread with a really thin layer of nut butter spread over it, cut into fingernail-sized pieces without any issues.
The main thing is to stay away from big blobs of these thick, sticky foods, rather than to avoid the foods altogether.
Foods With Lower Food Value When Other Food Is Available
Some foods are perfectly okay to eat, they just offer lower quality nutrition. These foods can be offered now and then, but generally, it is a better option to choose the more nutrient-rich alternative.
The following foods are usually better swapped out for one of the other foods listed:
- Lettuce (alternatives: rocket, watercress, and greens).
- Onions (alternative: garlic).
- Flavored cow’s milk yogurt (alternatives: plain live cultured yogurt or lactose-free plant-based yogurt but watch out for sugars and sweeteners).
- Cheddar and other full fat cheese (alternative: low-fat unflavored cottage cheese).
- Lower nutrient vegetables like celery and zucchini (alternatives: broccoli, tomato, squash, and sweet pepper).
- Honey (alternative: fruit for sweetness) – the exception is using good manuka honey for wound healing, where the rat is likely to lick it off over time.
- Green beans (alternatives: higher protein legumes like peas, chickpeas, and lentils).
- Crackers (alternatives: whole grain, sugar-free breakfast cereal, whole grain pasta, and egg noodles).
- Raisins (alternative: fresh grapes). Raisins have concentrated sugar and rats will often eat more of them because they don’t feel full (as they would from a fluid-filled grape).
There’s no real reason not to feed this group of foods other than there are more suitable or more nutritious alternatives.
And Finally – The Foods Your Rats Can’t Eat
A few foods should never be fed to rats because they are harmful to their health.
Fruit Pips and Stones
Apple seeds, peach stones, and other fruit pips contain a substance (amygdalin) which converts to cyanide in the stomach. The amount is small enough not to affect us humans, but as the lethal dose of cyanide is weight based, a rat could, in theory, be affected.
1-2mg/kg of body weight is enough cyanide to kill a mammal. The average rat weighs about half a kilogram, so would need 0.5-1mg to cause death. 1g of ground apple seed (about 1.5 pips) contains a variable amount of cyanide up to around 0.24mg depending on the variety.
So, while poisoning is unlikely – the rat would have to grind up and swallow between 3 and 12 whole seeds (depending on the variety), which almost certainly have a negative bitter taste, just as they do to us – it can’t be excluded unless you don’t include the seeds.
Peach, nectarine, cherry, plum and apricot stones are also affected, but poisoning is only possible if the stone gets ground and swallowed.
There is zero risk from the flesh of the fruit with the stone removed. The whole of a cherry stone only contains the same amount of amygdalin as an apple pip so, a small nibble on a stone would also have no effect.
Avocado Pits and Skin
While rats will benefit from having some avocado flesh in their diet, the stone and skin have always been shunned as they contain a toxin called persin, as well as a small amount of amygdalin (cyanide).
However, it’s hard to get a clear picture of levels of toxins in avocado skin and stone – and whether they affect rats at all. One rat guardian sought help when her rats ate half an avocado including the skin one-night and she was warned to expect the worst. However, the rats continued going about their lives without any adverse effect.
Toxicity, which seems to affect some species only, would lead to gastrointestinal irritation, diarrhea, possible respiratory distress, congestion, fluid the tissues of the heart, and even death.
A toxicity study on rats saw no toxic effect from high levels of powdered seed, and in another study where the powder was fed up to 8% of the diet, improvements in cholesterol, blood pressure and glycogen storage in the liver were noted.
However, we feel more evidence is needed before declaring avocado skin and stone to be safe for rats, so, for now, we’ve left it on the forbidden foods list.
Orange, Mango and Other Foods That Contain D-Limonene (Male Rats Only)
Male rats have a sex-specific protein in their kidneys that binds with d-limonene causing tiny protein clumps in the kidney. Over time these can develop into cancer.
While it’s unlikely that this will occur within the natural diet of a rat, it is possible that any clumping (even if reversible) would add to the vulnerability of the male rat’s kidneys to disease. So, it’s generally thought safer to avoid foods that contain large amounts of d-limonene altogether if you have bucks.
- All citrus fruit;
- All citrus fruit juice;
- Celery tops;
- Spices like pepper, ginger, and aniseed;
- All spice oils (which concentrate the d-limonene):
- Herbs like lemon balm and lemon mint (and their essential oils).
Just as for us humans, raw beans – particularly kidney beans – can be lethal if ingested, as they contain lectin-phytohaemagglutinin that causes red blood cells to clump together. Pulses fall into one of three categories:
- Those that can be eaten raw (lentils, peas, green beans, and edamame).
- Those that can be eaten raw if soaked and sprouted/baked (the above plus chickpeas, mung beans, and adzuki beans).
- Those that must always be soaked, boiled vigorously and cooked before eating. (mature/dried soya, black beans, haricot beans, red kidney beans, and all other large dry beans).
There is a toxic alkaloid called solanine which is found in potatoes where the skin has gone green. These should never be fed to rats and this extends to the flesh of the potato with the green skin removed, as the solanine spreads throughout. It is not destroyed by cooking.
Rats love food and most unprocessed food is safe for rats to eat, though some foods are healthier than others. You now know the few foods that rats can’t (or shouldn’t) eat, so why not check out our Ultimate Guide to the top 100 foods to feed your rats for more ideas of safe foods to give them.