How to Maximize Nutrient Absorption

Unhealthy lifestyle behaviors associated with an increased risk of premature death include smoking, excessive alcohol drinking, and not eating enough greens. The best way to get your greens is in whichever way you’ll eat the most of them, and one way to sneak extra greens into your daily diet is with whole-food smoothies, “a potent blend of good nutrition” in a quick, portable, delicious form.  

The Mayo Clinic offers a basic green smoothie recipe, combining the healthiest of fruits and the healthiest of vegetables, berries and dark green leafies, respectively. It calls for 2 ounces of baby spinach, which is about a cup and a half. Consider adding in some curly parsley, another mild beginner green to start with. Surprisingly, the sweetness of the fruit masks any bitterness from the greens such that the pickiest of children love these smoothies, as do adults who otherwise would not consume dark green leafy vegetables—or even fruit—for breakfast. Indeed, the average teen may only get about 1/20th of a serving of fruit otherwise—and Froot Loops don’t count. 

Offering smoothies can have a dramatic effect on fruit consumption for “students who do not want to take time peeling or chewing fruits.” (Who doesn’t have time to chew a fruit?!) The milkshake-y texture of smoothies may not only boost the quantity of fruit and vegetable consumption, but also the quality. 

Carotenoid phytonutrients, like beta-carotene and lycopene, can exist as microscopic crystals trapped inside the cell walls of fruits and vegetables. They’re only released when the cells are disrupted, which is why we have to chew really well. We either have to chew better or choose plants that are easier to chew. For example, while tomatoes have more beta-carotene than watermelon does, watermelon’s beta-carotene is more bioaccessible because its cell walls are wimpy compared with the smaller and tougher cell walls of other fruits and vegetables. To maximize nutrient release, food particle size would ideally be reduced to smaller than the width of the individual plant cells, but you can’t do that with chewing. Most vegetable particles end up greater than two millimeters when you chew them, whereas if we broke open all the cells, we could release much more nutrition, as you can see in my video, Are Green Smoothies Good for You?. The particle size distribution from chewing is about what you’d get blending in a food processor for about five seconds or one of those high-speed blenders for maybe half a second. Just 40 seconds in a blender can break down spinach to a subcellular level. 

Why does that matter? Let’s look at folate, the B vitamin in greens that is especially important for women of child-bearing age. Feed people a cup of spinach a day for three weeks and their folate goes up compared to control. What happens if you eat finely chopped spinach instead of whole leaves? You end up with more than twice as much in your bloodstream and the same absorption-boosting effect with lutein, the green nutrient so important for our eyesight.

It’s not what you eat—it’s what you absorb.  

The boost for lutein was only 14%, so a few extra bites of the whole leafy greens would have given you just as much. Some other nutrients, such as vitamin C, aren’t affected by pre-chopping at all. This is also less of an issue with cooked vegetables. If you boil carrots for three minutes, regular chewing can release about ten times more beta-carotene bioaccessibility than eating them raw, but not as much as blended. Intense cooking, like boiling for 25 minutes, so damages the cell walls so even gulping down large particles can result in significant absorption. But, blending may double carotenoid availability, explaining why we may be able to absorb three times the alpha- and beta-carotene from pureed cooked carrots compared to mashed cooked carrots. So, blending vegetables—raw or cooked—into soups, sauces, or smoothies can maximize nutrient absorption. Whether you went to the store and bought it, or toiled in your garden to grow it, you might as well take full advantage of it.  


Check out my other videos that touch on smoothies:

For other tips on getting children of all ages to eat healthier, see Tricks to Get Kids to Eat Healthier at Home and Tricks to Get Adults to Eat Healthier.

Finally, learn more about the effect of cooking on nutrient loss and absorption from these videos: Best Cooking Method, Raw Food Nutrient Absorption, and Sometimes the Enzyme Myth Is True.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Antioxidant- and Folate-Rich Foods for Depression

According to the Centers for Disease Control and Prevention, the rates of all of our top 10 killers have fallen or stabilized except for one, suicide. As shown in my video, Antioxidants & Depression, accumulating evidence indicates that free radicals may play important roles in the development of various neuropsychiatric disorders including major depression, a common cause of suicide.

In a study of nearly 300,000 Canadians, for example, greater fruit and vegetable consumption was associated with lower odds of depression, psychological distress, self-reported mood and anxiety disorders, and poor perceived mental health. They conclude that since a healthy diet comprised of a high intake of fruits and vegetables is rich in anti-oxidants, it may consequently dampen the detrimental effects of oxidative stress on mental health.

But, that study was based on asking how many fruits and veggies people ate. Maybe people were just telling the researchers what they thought they wanted to hear. What if you actually measure the levels of carotenoid phytonutrients in people’s bloodstreams? The same relationship is found. Testing nearly 2000 people across the United States, researchers found that a higher total blood carotenoid level was indeed associated with a lower likelihood of elevated depressive symptoms, and there appeared to be a dose-response relationship, meaning the higher the levels, the better people felt.

Lycopene, the red pigment predominantly found in tomatoes (but also present in watermelon, pink grapefruit, guava and papaya) is the most powerful carotenoid antioxidant. In a test tube, it’s about 100 times more effective at quenching free radicals than a more familiar antioxidant like vitamin E.  

Do people who eat more tomatoes have less depression, then? Apparently so. A study of about a thousand older men and women found that those who ate the most tomato products had only about half the odds of depression. The researchers conclude that a tomato-rich diet may have a beneficial effect on the prevention of depressive symptoms.

Higher consumption of fruits and vegetables has been found to lead to a lower risk of developing depression, but if it’s the antioxidants, can’t we just take an antioxidant pill? No.

Only food sources of antioxidants were protectively associated with depression. Not antioxidants from dietary supplements. Although plant foods and food-derived phytochemicals have been associated with health benefits, antioxidants from dietary supplements appear to be less beneficial and may, in fact, be detrimental to health. This may indicate that the form and delivery of the antioxidants are important. Alternatively, the observed associations may be due not to antioxidants but rather to other dietary factors, such as folate, that also occur in plant-rich diets.

In a study of thousands of middle-aged office workers, eating lots of processed food was found to be a risk factor for at least mild to moderate depression five years later, whereas a whole food pattern was found to be protective. Yes, it could be because of the high content of antioxidants in fruits and vegetables but could also be the folate in greens and beans, as some studies have suggested an increased risk of depression in folks who may not have been eating enough.

Low folate levels in the blood are associated with depression, but since most of the early studies were cross-sectional, meaning a snapshot in time, we didn’t know if the low folate led to depression or the depression led to low folate. Maybe when you have the blues you don’t want to eat the greens.

But since then, a number of cohort studies were published, following people over time. They show that a low dietary intake of folate may indeed be a risk factor for severe depression, as much as a threefold higher risk. Note this is for dietary folate intake, not folic acid supplements; those with higher levels were actually eating healthy foods. If you give people folic acid pills they don’t seem to work. This may be because folate is found in dark green leafy vegetables like spinach, whereas folic acid is the oxidized synthetic compound used in food fortification and dietary supplements because it’s more shelf-stable. It may have different effects on the body as I previously explored in Can Folic Acid Be Harmful?

These kinds of findings point to the importance of antioxidant food sources rather than dietary supplements. But there was an interesting study giving people high dose vitamin C. In contrast to the placebo group, those given vitamin C experienced a decrease in depression scores and also greater FSI. What is FSI? Frequency of Sexual Intercourse.

Evidently, high dose vitamin C improves mood and intercourse frequency, but only in sexual partners that don’t live with one another. In the placebo group, those not living together had sex about once a week, and those living together a little higher, once every five days, with no big change on vitamin C. But for those not living together, on vitamin C? Every other day! The differential effect for non-cohabitants suggests that the mechanism is not a peripheral one, meaning outside the brain, but a central one—some psychological change which motivates the person to venture forth to have intercourse. The mild antidepressant effect they found was unrelated to cohabitation or frequency; so, it does not appear that the depression scores improved just because of the improved FSI.

For more mental health video, see:

Anything else we can do to enhance our sexual health and attractiveness? See:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: