The World's Healthiest Foods

I enjoy the flavor of roasted nuts but am concerned that roasting may make nuts more difficult to digest or may damage nuts' healthy fats, resulting in the production of free radicals and causing nuts to become rancid more rapidly. Should I be concerned or can nuts be roasted without affecting their healthy benefits?

It's not clear in the scientific literature whether roasting affects nuts' digestibility or not, but a quick look at the basics of the digestive process may shed some light on this issue.

What Happens During Digestion

In the mouth, enzymes secreted in saliva begin the process of breaking down starch.

Next, enzymes released into the stomach primarily begin to denature, or undo the chemical bonds that hold proteins (amino acids) together.

Lastly, enzymes and bile secreted into the intestines finish the job by digesting fat, protein, and remaining starch.

Fiber, which is not digestible, mainly passes through the intestinal tract, although, bacteria that live in the large intestine (colon) produce enzymes that can partially break down certain fibers.

Starch is digested quickly-usually within 30 minutes to 2 hours-while protein takes a bit longer-anywhere from 1½ to 6 hours to digest-and fat takes much longer. Only about 10 grams of fat can be processed by the digestive tract per hour, so high fat foods or meals can take many hours to digest.

Nuts' Nutrient Make-up

Most tree nuts, with the exception of chestnuts, are very low in starch, high in protein and fiber, and very high in fat-healthy fat, but fat nonetheless. Depending upon the type of nut, the fat content can range from 54-70 percent. Nuts also contain quite a bit of protein, averaging from 13-18 percent, and nuts are rich in fiber, which comprises 4-13 percent of their nutritional content. Given this nutrient make-up, nuts are obviously relatively slowly digested-one reason they provide such a good source of long-lasting energy.

Other Factors that Affect Digestion

In addition to a food's nutritional make-up, other factors-such as cooking, the presence of certain compounds, and the type of protein it contains-can also affect the rate at which it is digested.

Cooking begins the break down of chemical bonds in food, which is why quickly cooking foods at low temperatures-the way foods are cooked in all the World's Healthiest Foods' recipes-can aid the body in being able to get the most nutrients from foods. Cooking at high temperatures breaks down even more chemical bonds, so many that it altogether destroys some of them, such as those that make up the fragile, heart-healthy fats in nuts.

Compounds such as polyphenols, tannins, phytic acid, and others can also affect the rate at which a food is digested. Nuts contain beneficial phenolic compounds, such as tannins, which are resistant to heat, so roasting does not begin the process of breaking them down. But although these phenols may take longer to digest, some have potent antioxidant activity that can help protect against heart disease by preventing the oxidation of "bad" LDL cholesterol.

Fiber, as noted above, is indigestible by us, but some types can be used by bacteria in the colon, and intestinal gas may result as a byproduct of their use.

The type of protein (amino acid linkages) also has an impact on a food's digestibility. In general, the scientific research indicates that plant food proteins are more digestible than animal proteins. More stomach acid secretion and more bile synthesis and secretion, and more pancreatic enzyme secretion is required to digest meats, and all of these "mores" mean digestive energy, digestive process, and digestive complexity. In addition, research has shown that plant protein is not, as some have thought, less usable by the body than animal protein. In fact, meat-eating subjects are much more likely to be in a state of nitrogen excess, i.e., trying to excrete the nitrogen residue of unused protein, than are vegans.

In a Nutshell

So, what conclusions can this information help us draw about the digestibility of roasted nuts? Roasting does help break down starch, so it's more easily digested, but since nuts have very little starch, this probably has little effect on nuts' digestibility.

Nuts are rich in plant protein. Research shows that cashew nut protein is broken down well by pepsin in the stomach, but that digestive enzymes secreted by the pancreas are less effective in breaking down cashew protein-unless the cashews have been cooked, so roasting may help improve the rate at which some nuts are digested.

Nuts are also rich in fiber which we cannot digest, but bacteria in our intestines can. Since a byproduct of their digestion of fiber can be gas, nuts' fiber can contribute not only to a feeling of fullness, but sometimes, to intestinal gas as well.

Perhaps most importantly, nuts are high in healthful fats, which compared to carbohydrate and protein, take a relatively longer time to digest.

The Bottomline: Nuts Digest Slowly

Nuts are not hard to digest; they just do not digest quickly. Because nuts contain considerable amounts of healthy fats, protein and fiber, they take a longer time to digest than carbohydrate-rich foods such as fruits, starchy vegetables or whole grain bread.

If a person eats more than one or two servings of nuts at one time-about 10 nuts equals one serving-it may seem as though the nuts are "heavy" in the stomach. But this feeling does not result from nuts being indigestible, but from the fact that nuts' nutrient composition means they naturally take a long time to digest. Plus, depending upon the milieu of bacteria in the intestines, the fiber in nuts may result in the production of a little gas, as mentioned above.

If you feel you have difficulty digesting nuts, we recommend that you lightly roast (as described below) these nutrient-dense members of the World's Healthiest Foods before eating-or enjoy a small serving of raw nuts to reap the maximum benefits from their healthy fats.

See our profile on Peanuts as an example of how roasted nuts are actually easier to digest and have more protection against the potentially harmful Aflatoxin mold. You can find the link to our Peanuts' profile under Eating Healthy, then WHFoods List A-Z. We hope you will enjoy all of the World's Healthiest Foods' nuts!

Because of their high content of delicate polyunsaturated fats, all nuts, whether roasted or raw, are susceptible to going rancid quickly. It is therefore important to either purchase nuts in their protective shell or if unshelled, from a store with high turnover to ensure freshness. Store nuts in your refrigerator or freezer. Generally, if stored in the refrigerator or freezer, nuts will remain fresh for 6 to 12 months. For more detail on how long specific nuts can be stored, please check the profile for the nut of your choice that is provided on the World's Healthiest Foods website.

If nuts have been stored longer than recommended, it's a good idea to throw them out. Rancidity sets in long before they smell or taste "off" or not fresh. Like oils damaged by exposure to high cooking temperatures, rancid oils contain free radicals that can cause cell damage in your body. To protect your body, avoid damaged oils of all types.

Roasting brings out the flavor of the nuts, and develops their sweetness. It is safe to roast nuts if done at a low temperature-typically a 160-170 degree Fahrenheit oven (at higher temperatures than this, research clearly shows damage to nuts' delicate fats) for 15-20 minutes will do the trick. Place nuts on a cookie sheet in a single layer. To enhance the "roasted" flavor, try putting a little Bragg's Liquid Aminos or soy sauce into a spray bottle and misting the nuts before roasting.

Avoid Commercially Roasted Nuts

Roasting nuts at a temperature higher than 170F will cause a breakdown of their fats and the production of free radicals. When nuts roasted at the high temperatures used commercially are consumed, the free radicals they contain can cause lipid peroxidation-the oxidizing of fats in your bloodstream that can trigger tiny injuries in artery walls-a first step in the build up of plaque and cardiovascular disease.

Check the Accurary of Your Oven's Temperature Gauge

To ensure you are actually cooking at the temperature you have chosen, we suggest you check the accuracy of the gauge on your oven, which can easily be done with an inexpensive oven thermometer. You can find an oven thermometer at any hardware or kitchen store, or even the kitchen equipment aisle of your grocery store. Look for a stainless steel, spring-operated dial type that has both a flat bottom for standing and a hook for hanging on the rung of an oven shelf. The cost is typically $5 to $12.

To test your oven, place the thermometer on a center rack, preheat the oven for 15 minutes, then compare the reading on the thermometer to your oven gauge. If it is higher or lower than what your oven gauge indicates, then you know your oven runs either hot or cold and can compensate. For instance, if your gauge reads 170F, but the thermometer reads 200F, you know your oven runs 30 degrees hot, and you can adjust temperatures accordingly.