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Health & Nutrition

Miscellaneous diet and health topics

Calories & metabolism

1. The calorie equation
2. Calorie diversion
   a. Protein use
   b. Other macronutrients
2. The carbohydrate equation
3. Nutrients per calorie
4. How calories turn into body fat
5. Appropriate percentages
6. Calorie-related disease
   a. Fatty liver disease

The calorie equation

A calorie is a measure of the energy that's available in food, which in turn supplies the energy that the body uses to carry out its functions or stores for future use.  We all have a general idea of what calories are, and the exact technical definition of the amount of energy in a calorie is not important for this article so I won't go into it. It's enough to know that an individual will gain body fat if the number of calories consumed is greater than the number of calories used, will maintain their weight if calories consumed = calories used, and will lose body fat if the calories consumed are less than the calories used.  If calories are underconsumed to the point that the individual runs out of body fat, the body will start converting muscle protein into the energy needed for physical processes.

All foods are governed by a basic equation where protein + carbohydrates + fat = 100% of the calories. These three food components are called macronutrients because they're present in food in relatively large quantities. The other components in food (like moisture, minerals, vitamins, and fiber) are calorie free, although there are some complications related to fiber that will be discussed in the section about the carbohydrate equation. Vitamins and minerals are called micronutrients because the amount in food is relatively small. 

Nature has limited the amount of protein in edible plants and animals. The non-dried, commonly eaten sources of whole animal protein top out at around 40% protein (see NutritionData results for beef, pork, poultry, seafood, lamb and veal, eggs and dairy). To go any higher than this natural limit, the food must be processed to remove some or all of the fat and carbohydrate content (or the moisture). Plant foods in general contain less protein than foods from animal sources. Most dried, non-processed legumes are less than 30% protein, with soybeans as the main exception at 40% high-quality protein (NutritionData). Seeds, nuts, grains, vegetables, and fruits are usually less than 25% protein (sometimes a LOT less), and most of them did not make NutritionData's list of the top 1,000 highest-protein foods.

Because of this natural limitation on protein, the fat plus carbohydrate portion of the equation will always be more than half of the total in foods that haven't had some major component removed.  The natural limits on the amount of fat and carbs that can be in a food are a lot looser, and in some foods the percentage of one or the other may be higher than 70%.

When one factor in the calorie equation has a lower percentage it means that at least one other factor has to have a higher percentage so the end result still adds up to 100%. The protein percentage is never going to be particularly high, so a plant food that's relatively low in fat automatically has to be higher in carbs and vice versa. That's just basic math.

All calories contain the exact same amount of energy. But that doesn't mean that all calories are created equal, because there's a lot of variation in the number of calories that the macronutrients deliver. Fat contains 9 calories per gram, while carbs and protein have 4 calories per gram. The body does not actually get that many calories from each gram of macronutrient because of the thermic effect of food - the energy that it takes to process these items. Fat is the easiest macronutrient to digest, carbohydrates are a bit harder, and protein is a lot harder.  The most commonly used estimate of the energy lost to the thermic effect is 2-3% for fat, 6-8% for carbohydrates, and 25-30% for protein (Jequier). At these rates, the actual calories absorbed are 8.73-8.82 per gram of fat, 3.68-3.76 for carbohydrates per gram of carbohydrate, and 2.80-3.00 per gram of protein.

This is not the only estimate of the thermic effect, and there are a variety of other rates out there. It is not known which estimate is the most accurate. In any, case the actual rate varies depending on factors like the characteristics of the food being eaten and the physical condition of the individual eating the food.

As an example of a different rate, Wikipedia shows rates of 5-15% for fat, 5-15% of carbohydrates, and 20-35% for protein, based on older studies. At these rates, the actual calories absorbed are 7.65-8.55 per gram of fat, 3.40-3.80 for carbohydrates per gram of carbohydrate, and 2.60-3.20 per gram of protein, which is not dramatically different from the previous estimate. No matter which guideline is used, it's clear that fat is much higher in calories than an equal amount of carbohydrates or protein on a per-gram basis.

The calorie counts on nutrient profiles and product labels have already been adjusted for the thermic effect, so we don't have to do any additional math when we're using existing calorie information.

Calorie diversion

The calorie equation assumes that all of the macronutrients consumed are converted into energy, but this is not the case with a normal (non-excessive) level of food consumption. A portion of the macronutrients will be diverted to other uses and will NOT be converted into energy. But the good folks who come up with the calorie counts don't know exactly how much will be diverted for any given individual at any given time, so they ignore this factor.  The calorie counts in nutrient profiles are the maximum amount of energy that you could obtain from the food, which is not necessarily the amount that you WILL obtain from the food.  If serious overeating is your hobby, you could actually end up turning all of those calories into body fat, because the body has already met its "other uses" needs at the point where enough eating starts turning into too much eating.  The rest of the discussion on calorie diversion assumes that food intake is not excessive.

Protein use

A significant amount of the protein in food is needed for other purposes in the body, so part of the potential protein calories will not actually be converted to energy. The amount of protein that ends up being used for energy will obviously vary a lot depending on factors like how much protein was eaten and how many specific amino acids it contained that were useable somewhere else. 

The biological value (BV) of a food estimates the percentage of its total protein content that will be incorporated into the body as protein rather than being used for energy. It looks like the BV of seeds, grains and beans falls roughly into the 60-80% range, with more of them probably closer to the bottom of the range than the top (Food-Info). There seems to be an implicit assumption that all the complete protein will be assimilated into the body tissues in protein form, and only the leftover incomplete protein will be converted to energy.

The accuracy of this assumption will depend heavily on whether the individual's protein consumption is within the normal range or is excessive. The acceptable crude protein range for humans is 10-35% (National Academies Institute of Medicine Food and Nutrition Board, WebMD), so the definition of "excessive" apparently starts at 35% for humans.  An acceptable range for birds hasn't been established, but it appears that the avian veterinary community is comfortable with the 30% level (Clinical Avian Medicine Chapter 4 Page 89). The cockatiel protein study by Koutsos et al considered 35% to be a high level at the outset, although they ultimately found that the birds tolerated a 70% level with no problems apart from some non-symptomatic liver lesions.  The Merck Veterinary Manual does not even object to the 70% level, but this is unnaturally high and definitely not recommended.  Due to the natural limitations on plant protein discussed earlier, almost all plant foods are less than 30% protein. The risk of a bird consuming more than 30% protein on a plant-based diet is essentially zero as long as you don't go for an all-soy diet or all-hempseed diet. Not getting enough complete protein from plant foods is a real risk however.

Based on the estimated biological value, the diversion of protein means that 60-80% of the potential protein calories have just vanished from the equation because the body has better things to do with the amino acids than burn them for fuel. The total amount of protein in the food hasn't changed, but we know that a large chunk of it will not actually be turning into calories.

The Protein article has additional information on amino acid needs.

Other macronutrients

There's also some diversion of fat.  The essential fatty acids (Omega 3 and Omega 6) are needed for specific body functions but can not be synthesized in the body and must be obtained from the diet. The daily amount needed for other purposes in humans is roughly 1-2 grams of Omega 3 fats and 5-7 grams for Omega 6 (Nutri-facts). In general, humans and pet birds who have enough food to meet their calorie needs will have no trouble at all meeting the Omega 6 requirement, and often exceed it by a wide margin. But it can be difficult to meet the Omega 3 requirement.   See the very end of the Fats & Oils article for information on the amount of Omega 3 needed for birds.

There is no diversion of carbohydrates; their only known function in the body is to provide energy. But as the next section explains, their contribution to the calorie equation is somewhat overestimated because indigestible fiber is included in the carbohydrate count.

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The carbohydrate equation

Pet food labels are legally required to show the minimum percentage of certain food components (protein, fat, moisture, and fiber).  They are not required to show the percentage of carbohydrates, so most of them don't show it.  It's fairly easy to compute the amount though.  You add up the percentages of protein, fat, moisture, and ash (minerals), and subtract this number from 100%.  The result is the percentage of total carbohydrates. There are a few complications however. 

For starters, most labels also don't tell you the percentage of ash. It looks like 3-4% is a reasonable estimate for most pellets. The ash content of whole grains is in the neighborhood of 1.5% (Joe Pastry). The ash content of beans is around 4-5% (Brigide et al Table 1, Strauta et al Figure 9). The grains usually seem to outweigh the beans by a significant margin in a bag of pellets, but there's usually some added minerals in the mix for nutritional purposes.  An estimate of 3-4% ash content in pellets seems reasonable, with an average value of 3.5%.  A level of 1-2% might be more appropriate for a seed mix that doesn't contain beans or added minerals.

The second complication is that the percentages on the label are the minimum values; it's likely that the actual value is higher.  To the extent that the label understates the percentage of the listed items, our equation will overstate the percentage of carbohydrates.

The third complication is that the percentage of total carbohydrates includes the fiber, which generally can not be digested by vertebrates but may or may not be digestible by intestinal bacteria to some degree (Clinical Avian Medicine Chapter 4 page 87).  The fermentation of fiber by bacteria may generate a small number of calories that can be used by the host animal (about 2 calories per gram of fiber) (Fiber Facts). But these bacteria-provided calories come from the fatty acids produced during the fermentation process, and are technically fat calories not carbohydrates (Linus Pauling Institute). The effect of these bacteria-produced calories is much smaller than some of the other uncertainties in our equation, so we can ignore it.

Although fiber is classified as carbohydrates, it does not provide any actual carbohydrate calories. If you're interested in the percentage of digestible carbohydrates (and we are), the results will be more accurate if you subtract the percentage of fiber from the total carbohydrate percentage that we calculated in the previous step (SFGate). I call this final number the net digestible carbohydrates; there may be a more appropriate technical term for it, but I don't have a good grasp of the advanced technical jargon involved with the estimation of carbohydrate energy.

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Nutrients per calorie

Which one delivers more nutrients per calorie - high fat-foods or high-carb foods? The answer is kind of mixed, but tilts toward the high-carb foods.

NutritionData has a Nutrient Balance Indicator (aka the completeness score) in all their listings that shows how far 1,000 calories of a particular food goes toward meeting the daily nutrient needs of humans. The high-carb foods (grains and beans/legumes) tend to outscore the high-fat foods (oil seeds and nuts).  Some selected scores for low-moisture foods, from lowest to highest:  walnuts 26, brazil nuts 32, brown rice 32, dry corn 34, cashews 36, millet 37, almonds 41, oats 42, peanuts 43 (remember, it's a legume not a nut!), barley 44, quinoa 45, wheat 45, sunflower seed 49, dry peas 53, lentils 57, soybeans 63.

Funny how the much-revered walnuts turned out to be the worst bargain on a nutrients-per-calorie basis, while some of the most despised foods in the bird world surpassed walnuts by a huge margin. Also notice that quinoa had the same score as plain old ordinary wheat - so much for its superfood status.

NutritionData has a listing for hemp seed, but it should not be used because it is seriously messed up.  Their listings usually match the USDA database, but something went wrong with hemp.  A lot of the information is missing, and the data that is there is dramatically different from the USDA listing.  This is unfortunate, because the completeness score for hemp seed is expected to be significantly higher than the score for sunflower seed.  The Tree Nuts section of the Seeds, Grains & Nuts article has the details.

This type of comparison really only works with low-moisture high-calorie foods, where eating 1,000 calories is something that can realistically be done and you have to be careful to avoid getting too many calories. High-moisture foods are so low in calories that you'd have to eat vast amounts of them to reach the 1,000 calorie limit. For example kale has a completeness score of 85 (wow!), but at 50 calories per 100 grams you'd have to eat 2kg (4.4 pounds) to actually achieve the promised nutrient level.

The unrealistic consumption levels needed for high-moisture low-calorie foods are the reason that I think the well-publicized study by DiNoia is misleading. This study determined that on a per-calorie basis, watercress was the most nutrient-dense of all foods. But this way of measuring things skews very heavily toward the ultra-low-calorie foods, which are generally very high in water and quite low in the absolute amount of everything else that's in them. That's why Table 1 of the study includes absurdities like iceberg lettuce being declared a more nutrient-dense food than winter squash and sweet potatoes. If you get stranded in the wilderness somewhere, a bag of sweet potatoes will keep you alive a lot longer than a bag of lettuce will.

The amount of nutrients per weight, volume, or bite is a much more realistic yardstick for high-moisture foods, since there is only so much that an individual can eat before they get full and have to stop. Measured this way, watercress is expected to be one of the least nutrient-dense foods because it's 95% water and you're only getting 5% solid material per bite. With kale you get 15% solid material per bite, and if you compare the nutrient profile for 100 grams of kale to 100 grams of watercress, you'll see that the kale delivers a lot more actual nutrients and is a much better use of your limited stomach space (use the drop-down box in the website listing to change the serving size to 100 grams). NutritionData gave watercress a completeness score of 86 - even higher than kale - but at 11 calories per 100 grams, you'd have to eat 9 kg (20 pounds) of it to actually get the desired result.

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How calories turn into body fat, and vice versa

The digestion process is somewhat different for protein, fat, and carbohydrates, but additional body fat is the end result of excess calorie consumption whether the calories originally came from fat, carbohydrates, or protein. Most of the incoming calories are from fat and/or carbohydrates, so they are the primary cause added body fat. Protein is the macronutrient of least concern when it comes to overeating issues because its contribution to the excess calorie load is far less than that of the fat and carbohydrates.

Carbohydrates are the body's "fast energy" source because they can be processed faster than protein or fat. Simple sugars are turned into energy faster than complex carbohydrates, which is the reason for the "sugar rush" and blood sugar spikes that occur when high-sugar foods are eaten. It takes much longer to process fats and protein, so these macronutrients provide a longer-lasting feeling of fullness than carbohydrates do.

During the digestion process, carbohydrates are broken down into glucose (a simple sugar that is the main fuel that the body runs on). The glucose that's needed for immediate energy needs is burned for fuel in a process that produces heat and an energy-carrying molecule called adenosine triphosphate (ATP) ( We don't hear much about ATP, but it's actually the primary energy currency of the cell (Wikipedia).

The glucose that is not used immediately is converted to glycogen (a complex carbohydrate that is the storage form of glucose).  This glycogen is stored in the liver and the muscles, and can be quickly converted to glucose when it is needed to meet the body's energy needs.  But the body's storage space for glycogen is rather limited, and when the storage space is filled to capacity the excess will be converted to fatty acids. 

Proteins are broken down into their component amino acids; the body diverts what it needs for other purposes and the leftover amino acids are converted into glucose, which then follows the same path as the glucose from carbohydrates.  Dietary fats on the other hand are directly broken down into fatty acids and other components, skipping the glucose/glycogen route. SANE has a nice diagram illustrating the process.

So excess calories from all three macronutrient types eventually end up as fatty acids, even though each one took a somewhat different route to get to that point.  The liver has played a major role throughout the process (PubMedHealth). The liver's next task is to convert those fatty acids into triglycerides (the form the body uses to store fat), and then off they go to be stored in the fat cells. 

This stored fat will only be used as an energy source after the body runs out of glucose and depletes its glycogen reserves. When the body needs to draw on this energy reserve, fat is oxidized to transform it into ATP (UPenn).

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Appropriate percentages

In any well-balanced plant-based diet for a pet bird, the percentage of carbohydrates is expected to be greater than the percentage of either protein or fats.  This is partly due to the natural limits on protein that were discussed earlier, and partly due to the fact that fats need to be limited because they have considerably more calories per gram than carbs do. 

Most plant foods have more carbohydrates than anything else, which naturally skews a plant-based diet toward having more carbohydrates than fats. But there are some plant foods (like nuts) that are much higher in fat, and the calories in these high-fat foods add up pretty fast. Many wild parrots naturally gravitate to a high-fat seed diet because they need a lot of calories to support their high-energy lifestyle.  But most pet birds don't get nearly as much exercise and can't afford that many fat calories (see Pet Birds & the Wild Diet article for more info on the difference in nutritional needs).

The calories in high-carb foods will add up too but not as fast as the fats, so an individual can eat more high-carbohydrate foods than high-fat foods without blowing the calorie budget. The high-carb foods tend to provide more nutrients per calorie than the high-fat foods do, which is obviously important.  This is discussed further in the "nutrients per calorie" section. 

The preceding discussion is mostly applicable to the nutrient-dense low-moisture foods that make up the bulk of a bird's diet, like grains, seeds, nuts, and beans/legumes.  Vegetables and fruits that are 80-99% water are so low in everything else that it's not very meaningful to describe them as being high in any of the macronutrients (protein, carbohydrates, and fat). But carbohydrates are usually the prevailing macronutrient in the high-moisture foods, and the carbohydrates in fruit tend to have a much higher proportion of simple sugars than other types of food (which is not a good thing). The Fruit article discusses the complicated relationship between fruit and parrots.

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Calorie-related disease

Inadequate calorie intake and excessive calorie intake can both lead to disease.  The reason that consistently not getting enough calories causes problems is pretty obvious:  the body needs a certain level of energy to function.  If it doesn't get enough energy from the diet, it will start using its own tissues as an energy source.  Muscle mass disappears, important functions become impossible, organs fail, and in the end there is death by starvation.

The food supply in the wild is erratic and unreliable, with periods where there's not enough food frequently alternating with periods where there's more than enough. To reduce the risk of starvation, evolution has made sure that the body is very efficient at storing unused calories during the good times to be used as an energy source during food shortages. But the food supply is a lot more plentiful and reliable in the affluent modern world than it is in the wild, allowing humans and their pets to accumulate large amounts of body fat that will never actually be needed.  Evolution didn't prepare us for this, so it causes a lot of health problems. 

It's not clear whether fats or carbohydrates play a bigger role in obesity and related health problems. There has been plenty of finger-pointing at both in recent years. Saturated fat has long been singled out as a special villain, but it may not be true (Authority Nutrition, Australian Food News).  Carbohydrates have been blamed too,  saying that foods with a high glycemic index may have a stronger influence on disease than high-fat foods  (Scientific American). But doubt has been cast on this too, and the glycemic index may be irrelevant for healthy individuals (Sacks et al, Daily Mail). It's possible to find recent studies on both fat and carbohydrates where the results are all over the place about which one is the culprit.  But regardless of whether either one is ultimately deemed to be the worst, there doesn't seem to be any doubt that overconsuming calories in general is the biggest part of the problem.   

Obesity is generally considered to be the #1 health problem in pet birds. According to Clinical Avian Medicine Chapter 4 page 91, "Obesity can lead to congestive heart failure or hepatic lipidosis [better known as fatty liver disease] and may predispose a bird to diabetes mellitus or exacerbate this illness." Atherosclerosis, xanthomas-lipomas-fatty tumors, and bumblefoot are other diseases in pet birds that are strongly correlated with obesity. Obese birds are more prone to arthritis, and obesity increases the risk of egg binding in hens.

It's thought that an unbalanced diet in general is a major cause of obesity in pet birds.  Although it appears that animals in general don't know when they're deficient in many nutrients, there is evidence that many (including birds) have a specific appetite for complete protein and will intentionally seek it out when they don't have enough in the diet (Steinruck & Kirchgessner, Murphy & King). Most seeds, nuts and grains do not provide enough complete protein per calorie to meet the need without exceeding the calorie budget for a pet bird, and this can lead to the bird eating more calories than it needs in order to meet the protein requirement. Nutritionally complete pellets provide an appropriate balance of protein and energy, and beans and legumes can be combined with seeds, grains, and nuts to raise the complete protein total.  See the Complementary Protein section of the Protein article for more information.

Fatty liver disease

Fatty liver disease is a fat buildup inside the liver cells caused by fats coming in faster than the liver can process them. These incoming fats represent the excess calories from all sources; it was explained earlier that unused carbohydrates and protein end up being converted to fatty acids, and unused fats stayed in the form of fatty acids all along. 

This fat buildup can cause inflammation and swelling in the liver, which can lead to damage that leaves the liver unable to function properly. Excess fat and carbohydrates are primarily blamed for the problem, since they contribute most of the excess calories (MedicineNet, Clinical Avian Medicine Chapter 15 Page 444 Hepatic Lipidosis section).

Protein deficiency is considered to be a secondary cause of fatty liver disease, especially methionine deficiency (Kumar et al, Mato et al, Livestrong).  In the case of protein, the FLD risk comes from not having enough, not from having too much.

It's often said that sunflower seed causes fatty liver disease, but this is not true.  Specific foods don't cause fatty liver disease, it's overconsumption of calories in general that does it. Fatty liver disease is described as a buildup of fat in the cells, not a buildup of sunflower seed phytochemicals.  Eating too many sunflower seeds could certainly lead to fatty liver disease, but eating too many tree nuts could do it even faster due to their higher fat content and lower protein content (see the Tree Nuts section of the Seeds, Grains, & Nuts article).

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