One of our top priorities in the kitchen is to prepare meals that are as nutrient-dense as possible. But we don’t want to give you meals that taste like they’re full of vitamin supplements! Luckily, we pick and choose our ingredients for flavor and nutrient content, and then prepare them using cooking methods that maximize those nutrients while optimizing flavor. How do we do it? We look at everything from the number of essential vitamins, minerals, and amino acids and then research the best ways to make those goodies available for our bodies to absorb. (We call this bioavailability.) Some foods, like meats and seafood, don’t need much work to make their nutrients accessible. Others, like vegetables, nuts, and seeds need a little extra effort.
What’s an essential nutrient?
Essential nutrients include any vitamin, mineral, amino acid or fatty acid that we cannot produce in our own bodies. They are best consumed in their whole form by eating real foods. Taking nutrient supplements can be a solution in a pinch, but supplements don’t necessarily take into account the ways in which the nutrient in question interacts with other foods. In other words, supplements can be either hard to absorb or they can create imbalances when they are too available. Nutrient content can vary drastically depending on the quality of the soil in which the food is grown or ways in which an animal is fed. For example, tomatoes grown in healthy, compost-rich soil can contain iron at quantities up to 1,938 parts per million, while tomatoes grown in weak soil may not contain any iron at all. Likewise, cows raised on grass are usually high in the vitamin A precursor beta-carotene and vitamin D, and they have a better ratio of omega-3 to omega-6 fatty acids than grain-fed beef.
How do we measure essential nutrients?
The most common way to talk about nutrient quantities in food is to refer to a food’s nutrient density. Simply speaking, nutrient density is the quantity of nutrients per volume of food. Nutrient density is most often concerned with essential nutrients and not all the other vitamins, minerals, fatty acids, amino acids, beneficial bacteria, and other goodies that we can manufacture in our bodies.
There have been many studies and ranking systems made over the last several decades to attempt to quantify and rank the nutrient density of commonly eaten foods. All of them have biases and drawbacks that result from their chosen unit of measurement. For example, Joel Fuhrman has developed a scale called the ANDI scale, which is widely used at grocery stores like Whole Foods. The ANDI scale measures the number of nutrients in a given food per calorie. Because it is calorie- based, this scale privileges foods that are low in calories. (Vegetables like kale that are high in nutrients and low in calories will get a much higher score than meats and fats, which are high in nutrients but also high in calories.)
Another nutrient density scale to consider is one developed by Mat Lalonde, a chemist and supporter of Paleo-style diets. Instead of using the calorie as a unit of measurement, Lalonde measures the number of nutrients per gram of food. Because this scale is weight-based, it takes calories out of the equation. Organ meats rank highest on his scale, followed by herbs and spices, nuts and seeds, cooked legumes, various muscle meats, cooked grains, vegetables, and fruits. However, it doesn’t take into account realistic serving sizes; for example, herbs and spices rank high on the list, but their score is based on a volume of consumption equal to that of meats and vegetables.
All of the scientists and nutritionists who have developed nutrient-density scores have acknowledged that it would be unhealthy to eat a diet that is made up entirely of high- scoring foods. High-scoring ANDI foods are all very low in fat, while Lalonde’s winners are heavy, rich, and lacking in fiber. Nutrient density is therefore more valuable as a tool for recognizing good sources of essential nutrients should your diet lack them.
Can we absorb all of these essential nutrients?
The biggest drawback to any of the current nutrient density scores is that they only take into account the amount of essential nutrients in a given food. They do not take into account our bodies’ abilities to absorb the nutrients. For example, raw whole grains contain a fairly high number of nutrients, but we would never eat them raw. Once they are cooked, many of these nutrients are diluted into the cooking medium. And if the grains have not been prepared properly, it will be difficult for our bodies to access even the nutrients that remain. In other words, it is essential to pay attention to the bioavailability of the nutrients in our food, not just the presence of these nutrients.
The bioavailability of macronutrients (carbohydrates, fats, and proteins) is usually not a problem. It is the micronutrients that are more susceptible to being underutilized in the body. All essential nutrients are considered micronutrients. Nutrients can be made more bioavailable in three ways: by selecting the most easily accessible and nutrient-dense foods, by improving preparation and/or cooking methods, and by serving the food with its proper accompaniments.
Selecting the right foods: There are many different sources of each of the essential nutrients. However, some sources are better than others. Take iron, for example. It is abundant in meat, fish, and leafy green vegetables, but it comes in a very different form in vegetables than meat. The iron found in meat is called heme iron. Its name comes from heme, a protective molecule that binds with iron. When heme iron is ingested, the heme molecule keeps the iron soluble in the intestine, which makes iron more easily absorbed by gut cells. On the other hand, vegetables contain non-heme iron, which lacks the protective molecule. Non-heme iron is less soluble in the intestine and is susceptible to modification by other foods in the diet. Only a small fraction of non-heme iron can be absorbed by gut cells. If you are anemic, it is far better to supplement with additional meat, poultry, and fish than to try and make up for iron loss simply with vegetables.
Improving preparation: Many plant foods contain substances called digestive inhibiting factors. These factors are used by plants to protect against predators (like humans!). Seeds have particularly high levels of inhibiting factors, which makes a great deal of sense from a biological perspective: plants cannot propagate if their seeds are being eaten and digested by predators. There are also digestive inhibitors (called oxalic acids) in many leafy greens and in nightshade vegetables.
Digestive inhibitors make it difficult to digest certain foods and often reduce nutrient bioavailability. These inhibitors often work in one of three ways: they transform the nutrient into form that is no longer recognized by its uptake systems in the gut, they bind with the nutrient to form a compound that can no longer be absorbed by gut cells, or they compete for the same uptake system as the nutrient in question. The structure of the vegetable cells in question can also be an inhibiting factor; some plants have rigid cell structures to protect their nutrients.
The primary digestive inhibitors in plant foods are as follows:
Phytate: Found in unrefined cereals, legumes, nuts, and oily seeds, phytate (or phytic acid) binds with ionic mineral compounds like zinc, iron, calcium, and magnesium, which makes them difficult to absorb.
Soybean protein: The soy protein found in certain varieties of unfermented soy can inhibit iron and zinc absorption.
Polyphenols: Some varieties of this compound (found in cereals, legumes, spinach, betel leaves, oregano, tea, coffee, and cocoa) form insoluble compounds with iron and reduce thiamin absorption. Others can bind with salivary and digestive enzymes and/or reduce the digestibility of starch, protein, and lipids.
Oxalic acid: Found in amaranth, spinach, rhubarb, yams, taro, sweet potato, sorrel, sesame seeds, and black tea, oxalic acid forms insoluble compounds with calcium and (sometimes) iron, making them inaccessible.
Dietary Fiber: Fiber is found in most plant products, and it can bind with bile acids, reduce fat absorption, slow digestion, and increase levels of gut bacteria (can be beneficial as well).
Luckily, there are cooking strategies to reduce and/or eliminate digestive inhibitors. Often chopping and/or cooking can free up many nutrients, especially those that are bound up in the cell structure of the plant. Cooking with heat also: deactivates certain protease inhibitors, amylase inhibitors, lectins, and oxalates in greens
increases the digestibility of proteins and starch (anyone who has tried to eat a raw potato knows the truth of this phenomenon)
potentially degrades phytates if the temperature is high enough
Other strategies require a little more advance work. Sprouting (or germinating) seeds and nuts increases the activity of enzymes called phytases. Phytases break down phytates, eliminating their inhibitory effect. Sprouting also reduces polyphenols in certain legumes, enhances non-heme iron absorption, and improves the digestibility of starches.
One of the most effective methods of reducing digestive inhibitors is fermentation. Fermenting can increase the bioavailability of non-heme iron in leafy greens and improve the bioavailability of nutrients in nuts, seeds, and legumes by eliminating phytates and lectins. In addition, the fermentation of grain-based breads by using a sourdough starter breaks down phytates. Individuals who are sensitive to free glutamate should exercise caution when fermenting anything high in protein.
As we mentioned above, there are a few vitamins (A, D, E, and K) that are only soluble in fat. That means that they are not bioavailable unless they are eaten alongside fats. Similarly, there are other foods that can improve the bioavailability of nutrients. The organic acids found in fermented foods improve absorption by forming soluble compounds with trace minerals. Ascorbic acid in citrus fruits, tropical fruits, strawberries, tomatoes, asparagus, and brussels sprouts makes certain iron compounds more soluble. Ascorbic acid can also counteract the inhibitory effect of phytate and may enhance the absorption of other trace minerals like selenium. Finally, animal protein enhances the absorption of zinc, iron, and copper.
Breaking Down Essential Nutrients
Now that we’ve laid out the basics of bioavailability, we can now consider the details of each essential nutrient. Keep in mind that each of these nutrients will have a different bioavailability depending on how food is prepared and served.
Vitamins are organic compounds that are vital to our health and cannot be produced in our bodies. (All vitamins are considered essential.) Conventionally, we when we’re talking about vitamins, we’re referring to those essential compounds that are not minerals, amino acids, or fatty acids. There are 13 recognized vitamins (or vitamin complexes), and they are named for letters of the alphabet.
Food processing and cooking always affects vitamin content. Steaming and waterless cooking methods generally preserve vitamin content better than boiling or braising. (Vitamins can be diluted by liquids and will often move out of the food and into the cooking liquid. If you choose to braise or boil foods, be sure to incorporate the cooking liquid into the meal so that you don’t miss out on those vitamins!) Oxidation is the primary cause of vitamin loss in cooking. There are, however, cooking methods that can make vitamins more available. Acidic cooking liquids tend to preserve vitamin quantities in foods better than alkaline liquids. In addition, the processes of culturing dairy, soaking and sprouting nuts and seeds, and lacto-fermenting vegetables make vitamins more accessible.
Vitamins have many different properties and biochemical functions. The most important property to consider is its solubility. Some vitamins, like vitamin C, are soluble in water, while others, like vitamin K, are soluble in fat. If a vitamin is fat-soluble, it needs to be eaten with some form of fat in order for the vitamin to be absorbed. Water-soluble vitamins present less of a concern, as they will inevitably be eaten in the presence of water.
Dietary minerals are elements that are required by living organisms other than carbon, hydrogen, nitrogen, and oxygen, which are present in common organic molecules. There are seven macrominerals that are used in great abundance in humans: calcium, chloride, magnesium, phosphorus, potassium, sodium, and sulfur. In addition, humans (and all other living organisms) need small amounts of what are called “trace” minerals. These trace minerals include iron, cobalt, copper, zinc, molybdenum, iodine, selenium, chromium, and manganese.
Minerals are most often eaten can be eaten in the form of a salt like sodium chloride, magnesium chloride, or calcium phosphate. When these salts are dissolved into water or another liquid, the salt compounds break apart into two ions. Once the minerals are ionized, the signaling systems in our guts determine which minerals are needed and which can be expelled as waste.
It is important to pay attention to the amount and method of consuming dietary minerals as certain minerals can compete and block receptor sites in the gut. For example, too much calcium may impede magnesium absorption. There are also certain substances in grains (phytic acid), greens (oxalic acid), and tea (tannins) may bind with ionized minerals and prevent their absorption in the gut. In addition, minerals can fail to absorb if there is a lack of hydrochloric acid in the stomach, an over-alkaline environment in the intestines, or a deficiency in enzymes and/or vitamin C. The best ways to consume minerals are mineralized water, unrefined sea salt, bone broth, and nutrient-dense foods and beverages.
All fats are made up of lipid compounds called triglycerides. Each triglyceride compound is composed of three fatty acid molecules connected to a glycerol molecule (a short 3- carbon chain that acts as a frame for the triglyceride). The fatty acid molecules are have two parts, shaped like a tadpole: an oxygen-hydrogen “head” and a long “tail” made from a chain of carbon atoms, each with one or two hydrogen atoms attached. Each fatty acid tail can be anywhere from 4 to 34 carbons long.
Fatty acids can be either saturated or unsaturated. Saturated fatty acids have the simplest hydrocarbon structure. In those fatty acids, every carbon in the tail has two hydrogens projecting from it. The term “saturated” refers to the carbons; each is holding onto the maximum number of hydrogens possible. Unsaturated fatty acids are slightly more complicated. In these fatty acids, the hydrocarbon tail has one or more “kinks” in it. Each “kink” results from the presence of a double-bond between two of the carbons in the chain. Each of these double-bonded carbons can each hold on to only one hydrogen. (In other words, they are “unsaturated” with hydrogen.) Monounsaturated fatty acids have one kink in their hydrocarbon tail; polyunsaturated fatty acids have at least two kinks.
Humans can produce almost all fatty acids in our bodies; there are only two essential fatty acids. Both are short-chain polyunsaturated fatty acids: omega-3 alpha-linolenic acid (ALA) and omega-6 linoleic acid (LA). However, there are other fatty acids (eicosapentaenoic acid (EPA), omega-3 docosahexaenoic acid (DHA), and omega-6 arachidonic acid (ARA)) that are categorized as “conditionally essential.” Healthy individuals should be able to synthesize these conditionally essentially fatty acids from ALA and LA. On the other hand, people suffering from disease or autoimmune conditions and those with sluggish digestive systems may have trouble making this conversion. Because these three fatty acids are generally better sources of health benefits than their shorter chain precursors, it is a good idea to eat foods that contain EPA, DHA, and ARA.
A word of caution: The standard American diet typically includes a high amount of omega-6 fatty acids, and often in the form of LA. It is important that we consume some amount of LA and other omega-6 fatty acids, but we shouldn’t overdo it. Conversely, most Americans lack omega-3 fatty acids. Ideally, we should be consuming omega-6 and omega-3 fatty acids at a ratio of at least 2:1, if not 1:1. For most Americans, that means really cutting back on omega-6 fatty acids and really increasing omega-3 fatty acids.
Amino acids are the molecular building blocks of proteins. They consist of anywhere from 10 to 40 atoms, which are mainly carbon, hydrogen, and oxygen. Every amino acid
must contain at least one nitrogen as part of an amine group (NH2); it is this group of atoms that give amino acids their name. Each protein molecule can contain up to hundreds of these molecules, and many proteins consist of a wide array of different amino acids.
Amino acids contribute flavors to food in two ways: First, they participate in browning reactions that create sweet, caramelized flavor. Second, some amino acids (like glutamic acid) have distinct flavors of their own. (We commonly refer to the flavor of glutamic acid as umami.) These flavorful amino acids only exhibit this properly when they have been released from their respective protein structure. Amino acids can be released from their protein structure when the proteins are denatured. Denaturation occurs when proteins are exposed to heat, high acidity, or air bubbles in water. These catalysts break the bonds between amino acid groups on the outer portions of the protein, which causes the protein to further unravel and expose more amino acid groups to the catalyst. When it occurs in the body, the denaturation of proteins is completely healthy. When it occurs via food processing, however, problems can occur. Read more about the problems about free amino acids in our post all about proteins.
Proteins that are not completely broken down during cooking need to be broken down during digestion in order for the body to absorb the amino acids. Proteins can be broken down in the stomach (high acidity), but they are also can be broken down via enzymatic activity.
There are about 20 amino acids that commonly occur in foods, and nine of them are considered essential.
The following charts lay out the sources and benefits of all of the essential vitamins, minerals, fatty acids, and amino acids. We’ve included a range of sources for each essential nutrient; it is important to keep in mind that some sources are better than others. Foods that are organic and non-GMO are going to be better sources than conventional produce. In addition, we’ve included sources like grains and soy in our list for the sake of full transparency. However, we find that foods like meat, fats, and vegetables are better (and more bioavailable) sources of these nutrients.
Finally, we need to note that these benefits haven’t all been approved by the FDA and we’re including them simply as an educational tool. For more information about the bioavailability of these nutrients in food, read our post on nutrient density.