Bioavailable, or BS?

We’ve spoken quite a bit about vitamins and other nutrients like polyphenols in previous blogs. Whilst it’s theoretically great if a product or ingredient contains a lot though, does that necessarily mean that we benefit from them?

It all depends on bioavailability, which is the degree to which the nutrients are available for absorption and utilization in the body. And this is impacted by a variety of factors, only some of which we can control.

Gender, age and life stage (eg pregnancy) can all play a role, for instance. As can the nature of the enzymes in our gastric juices [1]. So the bioavailability of nutrients in the same product eaten in the same way could be very different for you and a friend.

What we can control ourselves is how soon we eat it, how we cook it, how we eat it and what we eat with it.

How soon we eat something is the simplest to deal with. When it’s fresh produce, the sooner the better, because the nutrients degrade over time (as we can easily see). And they degrade particularly quickly once cut up, because they’re more exposed to heat, light and oxygen.

Freezing or drying the fresh produce locks in most of the nutrients, however, giving you longer to benefit from them.  The best method of preservation will depend on the food, as different ones behave in different ways.

Freezing apparently retains most of the nutrients found in raw cherries, raspberries and strawberries [2], for instance. But it isn’t as good for other fruits (including reducing vitamin C content [3]).

And dehydration has interesting effects on grapes. Whereas raisins apparently have fewer of some polyphenols and phenolic acids than grapes, for instance, total antioxidant and polyphenol contents remain relatively unchanged. And the phenolic acids appear to be more bioavailable in the raisins than the grapes. So the reduction in quantity is effectively offset by an increase in quality [4].

phenolic acids appear to be more bioavailable in raisins than grapes

It’s likely that every ingredient is affected in different ways depending on the preservation method. So eating a variety is key where possible, rather than just eating frozen berries, for instance.

Whether or not the food is cooked, and how, is a particularly important factor. It can impact the amount of nutrients in the food full stop, as well as the bioavailability.

Whilst some believe that eating food raw is best, it really depends on the food.

Although cooking can destroy some nutrients (particularly vitamin C), for instance, bioavailability is often enhanced by heat. On average, boiling apparently removes 14% of antioxidants. But averages aren’t particularly helpful here:

  • It boosts the antioxidant power of carrots and celery, for instance (cooking carrots increases the bioavailability of Vitamin A 6-fold over raw ones [5])
  • Beetroot and onions are hardly affected at all
  • But baking peppers can destroy as much as 70% [6]

cooking carrots increases the bioavailability of Vitamin A 6-fold over raw ones

That’s not to say that you shouldn’t bake peppers if that’s how you enjoy them most though, especially as you can easily boost the antioxidant power by adding spices in particular.

And some veg are actually potentially unsafe raw. Kale and spinach contain oxalic acid, which can cause stomach and kidney problems when taken in high doses. But heating breaks it down [7].

It’s perhaps no surprise that cooked and raw veg have different effects on different diseases. Raw may be slightly better for dealing with high blood pressure for instance [8]. But cooked have been found to have a greater impact on reducing the risk of some prostate diseases [9]. And whilst raw are better for dealing with most cancers, cooked are better from some [10].

Spices are also impacted by cooking – whereas cooked turmeric appears to offer better DNA protection, for instance, raw has greater anti-inflammatory effects [11].

So it’s best to vary your consumption of veg in particular between cooked and raw where possible.

it’s best to vary your consumption of veg in particular between cooked and raw where possible

In terms of how we eat the food, chewing it well is important.

Breaking down the cell walls and creating smaller particle sizes generally frees up the nutrients, and the same effect can obviously be achieved by cutting the food up.

This means there can definitely be a role for smoothies, especially if you wouldn’t eat a certain ingredient otherwise. But as noted in a previous blog, the sugar in them is “free”, and therefore potentially damaging. And drinking them quickly can disorientate the body and lead to higher calorie intake compared to eating the same ingredients as whole foods.

For a similar reason, juices are often suggested (by their manufacturers…) to be the perfect way of getting nutrients quickly. But as we’ve seen previously, the loss of fibre means that the product is probably missing a lot of the nutrients found in their raw ingredients in the first place (most micronutrients are bound to fibre and can only be liberated for absorption by friendly bacteria in the gut [12]).

the lack of fibre in juices means they’re probably missing out on a lot of the nutrients found in their raw ingredients

There is an exception to a general advice to avoid juices where possible, and that’s tomato juice. It apparently boosts the availability of lycopene five-fold over the whole fruit [13]. Studies show that it can rescue the immune function of subjects crippled by two weeks of fruit and veg deficiency, but neither carrot juice or spinach powder can [14].

And don’t forget that studies show chewing to be beneficial in itself (including being associated with a slimmer waist [15]).

Smaller particle sizes can be problematic with some foods however.

Studies indicate that when you make things like seeds and nuts into pastes, for instance, less of the food makes it to your gut for the bacteria to feed on [16], despite the fibre still being present. The smaller the particle size is, the more likely it is that our small intestines can digest it. This means there’s less food for the critical good bacteria in our large intestine. This has been found to be the case with flour, for instance [17]. So whilst minimising the size of an ingredient might increase the bioavailability of some of its nutrients, it may mean that you miss out on others completely, as they can only be liberated by gut bacteria.

the smaller the particle size is, the more likely it is that our small intestines can digest it, meaning there’s less food for the critical good bacteria in our large intestine

That’s not to say that smooth nut butters aren’t good for you at all of course. You’re just probably better off going for crunchy where possible (or at least a mix of the two).

Flax seeds are an exception to the general rule, however – they need to be ground for the body to be able to absorb their nutrients.

In terms of what we eat with the product in question, remember that vitamins A, D, E and K are fat-soluble. This means they’re best absorbed when eaten with fats. So if you’re eating kale, for instance (which is high in vitamins A and K). remember to include some fat in the meal too. You don’t need much though, and whole food sources like nuts or avocado are obviously preferable.

And the bioavailability of the infamous curcumin in turmeric is enhanced by black pepper.

So the bioavailability of the nutrients in natural, whole foods can vary a lot depending on a number of factors.

What about processed products with added vitamins and minerals, like a lot of snack bars?

Well we haven’t seen any studies specifically covering this. But as we covered in the last blog, we think this quote from The China Study is particularly apt:

Because nutrition operates as an infinitely complex biochemical system involving thousands of chemicals and thousands of effects on your health it makes little or no sense that isolated nutrients taken as supplements can substitute for whole foods.

And we don’t see how using added vitamins and minerals is any different to taking supplements. Especially as a lot of supplements are advertised as best eaten with food.

We’ll cover supplements more fully in a later blog, but there’s very little evidence of them being beneficial for most people, and in some cases they can actually be dangerous.

More importantly though, the fact that a snack product needs to have a whole host of vitamins and minerals added to it should be a warning sign that the rest of the ingredients probably aren’t that great…

the fact that a snack product needs to have vitamins and minerals added to it should be a warning sign that the rest of the ingredients probably aren’t that great

So just because a product has vitamin A as an ingredient, for instance, don’t bank on your body being able to benefit from it!

In conclusion, we believe that focusing your diet on a wide variety of whole plant foods and chewing them well is best. But there’s definitely a role for smoothies in small amounts, if you have the will power to drink them slowly! And that’s especially the case if they’re the only way you’d consume a really healthy food like kale, for instance.

Some of the prototype vedge bars were tested for vitamins and minerals over a prolonged period and the results showed that there was as much betacarotene (Vitamin A precursor), Vitamin E, potassium, manganese and phosphorous after 6 months as there was just after production (using carrots that had been dried over a year previously). Of the elements tested, only biotin (Vitamin B7) deteriorated over the period. The bars remained high (more than 20% of your RDA) in Vitamins A and E, and a good source (10 to 20% of your RDA) of potassium, manganese and phosphorous. And whilst the biotin content had deteriorated, the bars were nevertheless still a good source of it.

Because we use whole food veg, we don’t need to add anything to make them nutritious!

A quick note on phytic acid / phyates…

There’s a perception amongst some that phytic acid binds to minerals and makes them less bioavailable, so some foods are “activated” in order to remove the phytates and theoretically enable you to absorb more calcium, for instance. Some studies suggest that people eating more high-phytate foods have greater bone mineral density, however [18], and others suggest that phytates may inhibit the growth of cancer cells [19]. Rather than deliberately removing them, then, you might be better off eating more!

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