Monday, August 17, 2015

Thoughts on the Trans Fat Ban, Food Taxes and Carbon Emissions from Animal Agriculture

The Ban on Trans Fats

The FDA has decided to remove artificial sources of trans fats (aTFA) from the US food supply.  This began in 2013 Fred Kummerow wrote a citizen’s petition to the FDA to ban aTFA.  The petition was ignored, so he filed a lawsuit against the FDA.  The FDA responded and now plans to progressively remove aTFA from the US food supply which will be complete in 2018

One problem is the discussion of the health effects of aTFA usually begins and ends with it increasing LDL-C and decreasing HDL-C*.  This trivialises the health effects of aTFA, making it ‘a worse saturated fat’ in the eyes of the public, and turns it into something you can offset by taking unsaturated fats, phytosterols or drugs.  But the adverse health effects of aTFA go beyond increasing the total-C:HDL-C ratio.  Fred Kummerow has discussed some other mechanisms in his petition and some other papers he has written, but I suspect the story with aTFA won’t end there either

Despite the consistent body of evidence that aTFA are harmful, there have been some concerns about the ban, mainly about government intervention and personal freedoms.  I doubt the FDA will ban butter (for example) next because the US probation on alcohol (with alcohol being another easy to make substance that people want) was a pretty big failure.  I also doubt people actually want to knowingly consume partially hydrogenated oils over other fats or oils (that taste better and make you feel better)

Unfortunately it doesn’t seem like Australia or New Zealand will ban aTFA soon.  A spokesperson for the New Zealand Heart Foundation said that saturated fat is a bigger issue.  This ignores the evidence that SFA is not associated with CHD whether you look at its effect on cholesterol levels (unless you selectively use total-C or LDL-C and ignore the effect SFA has on HDL-C), meta-analyses of observational studies or the fact that there don’t appear to be any reduced SFA clinical trials**.  But whether saturated fat is a bigger problem or not is irrelevant to whether banning aTFA will improve health.  It is a false dichotomy that you have to choose between efforts to reduce saturated fat and banning trans fats

* aTFA has this effect by increasing the activity of cholesterol ester transfer protein (CETP).  Since genetic mutations of CETP have inconsistent effects regarding CHD and CETP inhibitors don’t reduce CHD, the adverse health effects of aTFA are probably not related to its effects on LDL-C and HDL-C

** All of the included trials in the recent Cochrane meta-analysis regarding reducing SFA for CHD were either SFA > PUFA, reduced fat or Mediterranean diet trials

Fat, Sugar and Salt Taxes

It has often been said that the ‘the western diet is high in fat, sugar and salt’, thereby blaming these nutrients for the high incidence of obesity and chronic disease in ‘western’ countries.  The blame is probably being placed on pizza and soft drinks (etc), but it could just as easily be placing the blame on eggs, cheese and fruit.  Grouping foods based on macronutrient composition and salt for the purposes of dietary research, recommendations or policy can sometimes be ineffective at targeting and discriminating between healthy or unhealthy foods

‘Good’ nutrients, ‘bad’ nutrients plays into the hands of the processed food industry who will adapt and reformulate their products to meet nutrient-based guidelines, taxes or food fads (see 3:29 of this video and note the low SFA chips), whereas the sellers of whole foods will be more strongly affected as they have a very limited capacity to adapt.  Adding or removing nutrients in processed foods is unlikely to achieve much, particularly if the nutrients themselves have a pretty neutral effect of health as is the case of fat, SFA and salt (unless they’re actually toxic such as aTFA and certain other food additives).  It’s still a processed food, low in nutrients and other beneficial substances.   A cake fortified with vitamins and low in saturated fat is still a cake.  It’s still low in protein, fibre, minerals, the vitamins they didn’t add, LCO3s, phytonutrients and zoonutrients and largely made up of refined starches, added sugar and added fats.  These ‘healthy’ reformulations by industry will be aggressively marketed and may give a bit of a green light (or a poor basis for rationalisation) for consumers to eat quantities of these foods as if they were actually healthy (an excellent example of this is all the low fat/low carb/low sugar/Paleo*/etc junk food).

A possible unintended consequence is that taxes that lower the consumption of certain whole foods will likely reduce the overall consumption of other nutrients associated with those whole foods.  For example a saturated fat tax would likely lead to reduced intakes of vitamin K2 (which is found almost exclusively in animal fats) and may also reduce intake of other nutrients like protein, iron and zinc (due to a lower consumption of meat), which most people could do with more of

With a large percentage of calories in the average western diet coming from processed foods, refined starches, added sugar and added fats, surely the focus should be on replacing these with whole, minimally processed foods regardless of macronutrient consumption (within reason)

All that being said, I’m currently in favour of a tax on sugar sweetened beverages (SSBs) (I’m undecided on fruit juice too as it’s more than just liquid sugar).  Nutrition education programs/initiatives, at least the way they are currently done, is proving to not be very effective.  Intensive nutrition advice, such as a 1-on-1 or small groups with the dietician/nutritionist, isn’t a long term solution as it will be expensive and people tend to revert to their old eating behaviours when that support is gone (such as in clinical trials).  Besides, consumption of SSBs remains high despite basically everyone thinking they are unhealthy.  This is unfortunate, as ideally education would be sufficient to change behaviour, but I only need to look at myself to realise that’s not the case.  Real life is not as black and white as that and environmental pressures can be powerful even when you’re conscious of them.  A tax on SSBs is likely to reduce consumption and slightly improve health or at very least provide some funding for healthcare, and there shouldn’t be much risk of unintended consequences.  Some people may just switch to artificially sweetened beverages, which may or may not be a healthier choice and probably depends on which sweetener is used

* Paleo is not the sum total of grain free, dairy free and sugar free and in my opinion ‘Paleo’ cupcakes (and other baked goods and desserts) is an oxymoron

Carbon Emissions from Animal Agriculture and Conservation of Carbon

Food sustainability is becoming more commonly discussed, such as the new USDA dietary guidelines (discussed here), Sweeden’s dietary guidelines and also in a recent paper looking at the effects of a CO2 tax.  There are a few key issues in these discussions of sustainability including the obvious (overfishing and eating local and season food) and the idea that high consumption of animal foods is not sustainable

There are many components to ‘sustainability’, but perhaps the main reason animal foods are singled out is for greenhouse gas emissions, where animal foods are proposed to emit more greenhouse gases than plant foods.  However, some aspects of this idea don’t make much sense in the context of animals on pasture (CAFOs are obviously absurd), though I can understand how this idea may have come about

To begin with, another argument against animal foods is that much more water is needed to produce a kilogram of beef (for example) compared to a kilogram of plant food.  I’ve been very sceptical of relevance of this claim because it’s not like this water is lost, but rather almost all the water is excreted as urine.  Think about us: if we drink 2 L per day and live for 75 years, that means we drink about 55,000 L in a lifetime.  Where does that water go?  Almost all of it leaves our body in urine and sweat and we only hold onto a very small amount of that water, about 0.1%.  So long as the consumption of water exists in a closed system or is sourced sustainably then the higher water requirement shouldn’t be a problem as the water isn’t lost and just gets recycled.  However, excessive irrigation water from rivers or lakes in drought prone areas is definitely a problem (such as the Murray-Darling basin)

This leads to the greenhouse gas issue.  Very simply, plants take CO2 from the atmosphere (and water from their roots) and convert it into carbohydrates like glucose.  Animals eat the plants and extract energy from glucose first by breaking down the glucose molecule into carbons and hydrogens, where the carbon atoms are combined with oxygen to form CO2 and are removed from the body.

Imagine in a closed system like a biosphere where grass grows by taking up atmospheric CO2, cows then eat the grass and release almost all of the carbon via respiration.  In isolation, if the carbon stored as biomass (grass + soil + cows) is identical from year to year, then atmospheric carbon must also be identical.  However, atmospheric carbon will increase if the cows overgraze in this biosphere due to less carbon being stored as biomass as there will be less carbon stored as grass and not an equivalent increase in carbon stored as biomass in the cows as most of the carbon the cows eat is exhaled as CO2 (this cycle is occasionally mentioned, but I think it needs to be reinforced)

Two laws of physics include the ‘conservation of energy’ and the ‘conservation of mass’.  I think we need a similar law here, the law of ‘conservation of carbon’

With carbon being conserved, agricultural systems that store more carbon as biomass (usually in the form of topsoil and plants), such as include perennial crops (fruits, nuts and legumes) and managed grazing would reduce atmospheric carbon.  While those systems that deplete this biomass, such as annual crops due to tillage and systems with high oil use (transport, fertiliser, etc), would increase atmospheric carbon.  Why then is animal agriculture portrayed as being so harmful for the environment?

Higher carbon flux: people seem to only measure and report the rates of CO2 released into the atmosphere.  This is understandable because the increase in atmospheric carbon appears to be mostly driven by the release of stored carbon due to deforestation and the burning of fossil fuels.  However, without also measuring and reporting the rate of carbon taken up in a system you can’t know the overall balance of carbon.  If only CO2 emissions are being measured and not also CO2 uptake, then a carbon neutral system with higher carbon flux would appear worse than carbon neutral system with lower carbon flux.  Animals grazing on rapidly growing plants like grass would almost certainly have a higher carbon flux than most other forms of agriculture based on: growing plants having a higher net rate of CO2 uptake (to support growth) compared to mature plants; and that animals have a higher metabolic rate than plants.

Methane: another reason is for the focus on animal agriculture is the methane released from animals, particularly ruminants.  Methane is formed by enteric fermentation, where carbohydrates are broken down by microorganisms in an anaerobic environment (such as the rumen in ruminants), which actually occurs to a greater extent if the animals are fed grass.  Less methane released compared to CO2 and there is less methane than CO2 in the atmosphere.  However, methane is a more potent greenhouse gas (~20-30x depending on source), but has a shorter half-life (~2-10 vs. 50-200 years depending on source).  So it’s argued that reducing the release methane from livestock would be an effective quick fix for climate change, giving us more time to reduce other greenhouse emissions (assuming that happens sufficiently).  But how much of impact does enteric fermentation actually have?  Enteric fermentation has been estimated to contribute to about 13% of global methane released between 2000-2009 [1] or 26% of US methane released between 1990-2013 [2].  Currently methane contributes about 9.5% of CO2 equivalents of greenhouse gases in the atmosphere* (calculated from [3]), so the enteric fermentation contributes 1.2% to total global or 2.5% to US greenhouse gases.  This may very slightly (probably a few percent) overestimate the impact of enteric fermentation as the carbon originally came from the atmosphere.  And of course, this doesn’t reflect animal agriculture as a whole as enteric fermentation is only one component and other relevant issues include oil use, whether deforestation occurred and the effect on topsoil.  Therefore, while enteric fermentation is a notable source of greenhouse gases, I think its role has been over-exaggerated and the question of whether this meat is sustainable is probably more related to farming practices and transportation

* I don’t think it is correct to calculate the contribution of methane from enteric fermentation to overall greenhouse gases by using rates of methane emitted relative to CO2 and other greenhouse gases.  This is because the relevant measure to compare the contribution of different gases is the concentration of the gases in the atmosphere rather than how many CO2 equivalents of each gas is emitted.  Calculating the contribution of methane (including enteric fermentation) by using methane emissions (which is what often happens) overestimates the contribution as methane has a higher relative flux than CO2.  To use an extreme example to make a point, imagine you have gas A and gas B with the following characteristics.  Clearly gas B contributes more to the overall concentration of gases at year 10 even though gas A has a higher flux.  However, in this example, reducing emissions of gas A by X% is likely to be more effective than reducing emissions of gas B by X% to reduce the overall concentration of gases.


Gas A
Gas B
Concentration year 0
100
100
Emissions per year
50
30
Degradation per year
45
5
Concentration year 10
150
350

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