Two recent studies on avocados have made this dietitian start eating more.

The first was conducted at Ohio State University and examined whether eating avocado could increase vitamin A levels in the blood after meals (1).

Vitamin A is obtained from plant foods by eating carotenoids which the body can then convert into vitamin A. There is evidence that adding fat to meals can increase carotenoid absorption, which isn’t surprising given that carotenoids are fat-soluble. (See the VeganHealth.org article about Vitamin A for more info.)

The study showed that not only did adding 1/2 of an avocado to a high-carotenoid meal increase the amount of carotenoids absorbed, it also increased the amount of vitamin A in the blood by about 3 to 6 times compared to a high-carotenoid meal without avocado.

Some caveats:

– It’s not clear that the amount of vitamin A measured in the blood after a meal really indicates that someone has better vitamin A status.

– Some people are, apparently, “non-responders” and do not absorb more carotenoids when added to the diet. In this study, one participant (out of twelve) was found to be a non-responder and she was removed.

– The Hass Avocado Board provided some of the support for this study.

Increasing vitamin A isn’t necessarily needed by most people, but since vegans do not get a direct source of vitamin A, and many may not eat enough carotenoids, adding avocado to meals will help ensure that you’re efficiently utilizing carotenoids.

And why not? Avocados are delicious.

Of course, there is a reason why not – because avocados are high in fat.

It turns out that due to their high water and fiber content, avocados barely rise to the category of a medium energy dense food. A serving size is considered 1/2 of a medium-sized avocado or 70 g. One serving contains 4.6 g of fiber, 10 g of fat, but only 112 calories. As an extra bonus, it contains 340 mg of potassium (almost as much as a medium-sized banana).

This brings us to the second study, from Loma Linda University, looking at energy intake and satiety (feeling satisfied) when avocados are added to the diet (2).

There were three test meals: a control lunch without avocado, a lunch with the same amount of calories as the control lunch and including 1/2 of an avocado, and a control lunch plus 1/2 of an avocado.

The lunches with the avocados resulted in slightly less hunger over the next three hours, and the people who ate avocados with lunch ate less calories for their evening meal and snack (1194 vs. 1276 kcal; difference was not statistically significant). The meals in which avocado replaced other calories were the winners as those people ate 83 calories less for the day.

Again, there are caveats:

– This doesn’t mean that eating an avocado every day will lead to weight loss. At the very least, it’s evidence that adding one-half of an avocado a day won’t lead to eating more calories for most people.

– In the words of the authors, “The funding for this study was supported by a grant from the Hass Avocado Board, which had no role in the design and conduct of the study; in the collection, analysis, and interpretation of the data; or in the preparation, review or approval of the manuscript.”

Any time a study is supported by an industry group you have to be more skeptical. Even if the Hass Avocado Board had nothing to do with conducting the study, there may be an unconscious bias for a positive analysis. In this case, the Loma Linda University researchers suggest that a longer trial is needed “to evaluate the effects of daily avocado intake on measures of appetite sensation and weight management in free-living normal weight, overweight and obese adults.” In other words, it would be great if the Hass Avocado Board could fund some more research.

But that said, who else is going to fund studies like these? We might have to wait a long time before the government makes studying avocados a priority.

When I go to Chipotle, which is every few weeks, I normally ask them to really limit the guacamole they add. It can be comical how large the servings there get as ingredients pile up and by the time they get to the last item, the guacamole, there is already a massive amount of food on the tray, so I’m not inclined to change my ordering habits there.

But Chipotle aside, the research above has already made me add more avocado to my daily eating habits. Congratulations to the Hass Avocado Board – you’ve made a believer out of me!

References

1. Kopec RE, Cooperstone JL, Schweiggert RM, Young GS, Harrison EH, Francis DM, Clinton SK, Schwartz SJ. Avocado Consumption Enhances Human Postprandial Provitamin A Absorption and Conversion from a Novel High-β-Carotene Tomato Sauce and from Carrots. J Nutr. 2014 Aug;144(8):1158-66. | link

2. Wien M, Haddad E, Oda K, Sabaté J. A randomized 3×3 crossover study to evaluate the effect of Hass avocado intake on post-ingestive satiety, glucose and insulin levels, and subsequent energy intake in overweight adults. Nutr J. 2013 Nov 27;12:155. | link

Based on some articles that were floating around the Internet suggesting that vegan infants might be at risk for vitamin A deficiency, I asked Reed Mangels, PhD, RD what evidence we have that the breast milk of vegan mothers is adequate in vitamin A. She wrote an article about it and posted it in the Vegetarian Resource Group’s blog:

Vitamin A and Breastfed Babies

Excerpt:

“The bottom line – Vegan women who are breastfeeding should make sure that their diet includes good sources of precursors of vitamin A. These are foods rich in beta-carotene such as winter squash, carrots, pumpkin, sweet potatoes, cantaloupe, and green leafy vegetables. Dietary fat is needed to promote beta-carotene absorption so it is important that lactating women not overly limit dietary fat.”

Following up on the post, White Blood Cells in Vegans, I came across two more pieces of info.

The Linus Pauling Institute says, “Vitamin A and retinoic acid play a central role in the development and differentiation of white blood cells, such as lymphocytes, which play critical roles in the immune response (1).”

Unlike omnivores, vegans do not have a direct, dietary source of vitamin A, but rather get it indirectly via carotenoids (mainly beta-carotene). Beta-carotene is fat-soluble. It seems theoretically, possible then, that a low intake of carotenoids or fat could contribute to lower vitamin A status and white blood cell count (WBC).

This is purely hypothetical; to my knowledge vitamin A levels have not been measured in vegans and other signs of low vitamin A status have not been a noted problem. Anecdotally, I had been eating plenty of beta-carotene and fat at the last measurement of my WBC which showed them to be below normal.

Paul Appleby, of EPIC, passed on a study to me of a clinical trial using a “Daniel Fast” from the University of Memphis (2). In this trial, mostly healthy and some vegetarian subjects (13 men, 30 women; 20-62 years old) went on a Daniel Fast for 21 days, eating no processed or packaged food and only plant foods (as much as they wanted). Their WBC went from an average of 5.7 to 5.0 (2). 5.0 is within the normal range, but on the lower end (normal being about 3.5 to 12.5 billion per liter).

The authors of the Daniel Fast study say, “It has been suggested that ingestion of food additives and preservatives can increase white blood cell count by triggering an immune response due to a sensing of invading pathogens from the food stuff; however, we are unaware of any scientific reports that confirm this hypothesis.” I should point out that lots of things have been suggested, but it doesn’t seem impossible that vegans generally eat less food additives and preservatives and this could be contributing to low WBC.

I have added this information to VeganHealth’s article on White Blood Cells.

There were some other interesting things about this study. Here are the before and after (or during in the case of the nutrient intakes):

calories: 2,185 → 1,722
fat (g): 74 → 54
fat (%): 30 → 27
saturated fat (g): 24 → 9
cholesterol (mg/dl): 171 → 139
LDL (mg/dl): 98 → 76
weight (lbs): 171 → 167
bp: 115/72 → 106/67

The authors did an analysis which showed that the improvements in these parameters did not occur in only the unhealthier subjects, but rather across the board. They say, “It is interesting to note that even those subjects who were vegetarian prior to starting the fast experienced dramatic reductions in total and LDL-[cholesterol], in addition to improvements in other markers. Clearly, the exclusion of meat from the diet (as is the case for vegetarians) is not the only dietary factor involved in raising circulating cholesterol and other risk factors for cardiovascular and metabolic disease.”

It should be noted that this trial had no control group and was not randomized in any way.

I found this interesting because even though the subjects didn’t lose much weight (the weight change wasn’t even statistically significant), their blood pressure and cholesterol levels went down substantially in only 3 weeks. That’s impressive. But does it mean that it is the diet that everyone should be on all the time, indefinitely?

Stay tuned.

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Reference

1. Linus Pauling Institute. Micronutrient Information Center. Vitamin A. Accessed 5/20/13 | link

2. Bloomer RJ, Kabir MM, Canale RE, Trepanowski JF, Marshall KE, Farney TM, Hammond KG. Effect of a 21 day Daniel Fast on metabolic and cardiovascular disease risk factors in men and women. Lipids Health Dis. 2010 Sep 3;9:94. | link

Vitamin A is found only in animal products, but the body can create it out of carotenoids, like beta-carotene.

When I first got involved in vegan nutrition, vitamin A was considered a non-issue because we assumed most vegans would easily get enough beta-carotene with any sort of varied diet to cover our needs.

But in 2001, the Food and Nutrition Board (FNB) doubled the amount of beta-carotene they said was enough to meet vitamin A needs. According to the FNB, this change was based on “data demonstrating that the vitamin A activity of dietary β-carotene is one-sixth, rather than one-third, the vitamin activity of purified β-carotene in oil (1).”

They go on to say:

“This change in bioconversion means that a larger amount of provitamin A carotenoids, and therefore darkly colored, carotene-rich fruits and vegetables, is needed to meet the vitamin A requirement. It also means that in the past, vitamin A intake has been overestimated.”

This change mostly flew under the radar, but it made a significant difference in how easy it would be to get enough beta-carotene.

I recently became more concerned about vitamin A, quite literally, by accident. Early last Fall, I twice got up in the middle of the night and walked straight into my bedroom door that was halfway open, face-first!

Over the previous year or so, I had slacked off on vitamin A, relying only on a bit of shredded carrots on salad and mangoes on most days. In mid-November, I decided I needed to make a real effort to add more yellow vegetables to my diet and started eating sweet potatoes every day. A few weeks later, I realized that I had been having no trouble seeing the bedroom door at night. I wondered if there was a connection to what seemed to be my improved night vision.

In checking out whether it was likely that my apparent change in night vision was possibly caused by eating more beta-carotene, I was reminded that vitamin A metabolism is involved with immune function. When vegans get sick easily, I tell them to think about more zinc or protein, neglecting any concern about vitamin A. (Interestingly, vitamin A metabolism appears to rely on zinc.)

Vitamin A deficiency symptoms begin with night blindness, and if it progresses, can lead to the more severe eye problems of corneal ulcers, scarring, and blindness (2). Vitamin A is also important for growth and development in infants and children, and for red blood cell formation (2).

Because I suspect that many vegans might not be giving vitamin A any thought, I decided to make this post and add some information to Vitamin A at VeganHealth.org. That link has a chart showing which foods are high in carotenoids. I would encourage everyone to check the chart to make sure they are getting enough. And you might save yourself a few bumps on the noggin!

References

1. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: The National Academies Press, 2001. | link

2. Vitamin A. Linus Pauling Institute. Accessed 1/25/2013. | link

Fat Soluble Vitamins: Do They Stand Between Vegans and Health?

When I made my original post about plant food sources of vitamin A the other day, I completely forgot the largest source of all: carrot juice!

Carrot juice contains over twice the RDA in one cup – 2,256 RAE.

And I’ve added a few more foods to the Vitamin A page on VeganHealth.org.

A nutrient not many people think a lot about is vitamin A. I just updated VeganHealth.org with the vitamin A content of various plant foods. Take a look there and make sure you’re getting enough!