Bioavailable, or BS?

We all know that it’s important to get our vitamins and minerals. And previous blogs have discussed how veg, for example, are a great source of them.
But just because an ingredient or product contains them doesn’t mean we can actually benefit from them. 
It all depends on bioavailability.
That’s 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.

What determines bioavailability?

Gender, age and life stage (eg pregnancy) can all play a role. 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 are:
  1. how soon we eat the food;
  2. how we cook it;
  3. how we eat it;
  4. what we eat with it; and
  5. our diet in general

1 – Timing

With fresh produce, the sooner we eat it the better. That’s because the nutrients degrade over time (as we can easily see when guacamole goes brown). And they degrade particularly quickly once cut up, because they’re more exposed to heat, light and oxygen.
Freezing or drying the fresh produce can preserve most of the nutrients, though, giving you longer to benefit from them.  The best method of preservation will depend on the food, however, 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]).
  • Drying
    • Has interesting effects on grapes (and probably other foods too). 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].
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.
And whilst prepared products like ready meals and snacks are often preserved in various ways, it’s nevertheless best to eat them as soon as possible.

2 – Cooking

Is raw best?
It really depends on the food. Although cooking can destroy some nutrients (particularly vitamin C), for instance, bioavailability is often enhanced by heat:
  • Boiling carrots increases the bioavailability of Vitamin A 6-fold over raw ones, for instance [5];
  • But baking peppers can destroy as much as 70% of their nutrients [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. Eating them baked is better than not eating them at all. And 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, for instance. But heating breaks it down [7].
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”

3 – How we eat the food

Is eating a whole piece of carrot best?
Depending on the circumstances, we do think that chewing a whole piece is generally best.
  • First, chewing stimulates the production of saliva, whose enzymes start to break the food down.
  • Second, it signals to the body to begin the digestion process, so it prompts the production of stomach acid for example.
  • Third, it breaks down the cell walls to create smaller particles,  generally freeing up the nutrients and improving bioavailability.
  • Fourth, studies show chewing is beneficial in itself, such as being associated with a slimmer waist [15]
What about smoothies and juices?
The benefits of smaller particles mean there can definitely be a role for smoothies too. Especially if you wouldn’t eat a certain ingredient otherwise. But:
  • As discussed in a previous blog, the sugar in them is “free”, and therefore potentially damaging.
  • Drinking them quickly can disorientate the body and lead to higher calorie intake compared to eating the same ingredients as whole foods.
  • And even if you drink them slowly, the body isn’t as well prepared as if you’d had to chew the whole food instead.
Juices are generally worse though.
The even smaller particle sizes can make them a great way of getting nutrients quickly. But 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. That’s because most micronutrients are bound to fibre and can only be liberated for absorption by friendly bacteria in the gut [12].
And the potential problems with smoothies (such as free sugar) are even more relevant for juices.
“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 though, 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].
Are smaller particle sizes always good for bioavailability?
No – they can actually be problematic with some foods.
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]. The smaller the particle size is, the more likely it is that our small intestines can digest it. Which 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 smaller particles might increase the bioavailability of some nutrients, you may 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 seed rule, however – they need to be ground for the body to be able to absorb their nutrients.

4 – What we eat at the same time

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.
In any event it’s generally best to eat as varied and nutritionally balanced a “meal” as possible, even if it’s just a snack. 

5 – Our diet in general

Even if you’ve done everything “right” so far, there’s a still a final consideration. And that’s our microbiome, or the bacteria in our gut.
They determine the nature of the enzymes in our gastric juices [1] (which break our food down). And they impact the bioavailability of some nutrients.
So if you don’t have the right bacteria, you might not benefit from some nutrients at all. Everyone will be different in this regard, but the wider the variety of plants you eat, the healthier your microbiome is likely to be. And the more benefit you’ll get from the food you eat (a nice, virtuous circle!).

We’ve focused above on natural foods, but 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 in a future post, 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, if a product needs to have a whole host of vitamins and minerals added, it should be a warning sign that the rest of the ingredients probably aren’t that great…
“if a product needs to have a whole host of vitamins and minerals added, it should be a warning sign that the rest of the ingredients probably aren’t that great”

In conclusion

Overall, 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.
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! Or at least have a mix of “normal” and activated ones.


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