In developing countries, increases in palm oil consumption are associated with higher mortality due to ischemic heart disease (IHD) to a greater degree than in countries that have been historically wealthy. These increases occur above and beyond those caused by smoking and other important economic, demographic, and nutritional trends.
Global palm oil consumption represents an important health policy challenge. The consumption of palm oil overtook soybean oil consumption globally in 2003, and the increasing price competitiveness of palm oil relative to soybean oil has resulted in palm oil's status as the dominant oil on the global market . The world market for palm oil is forecast to surpass 100 million metric tons by 2015, fueled primarily by demand in growing economies such as China and India . Their future palm oil consumption could potentially increase cardiovascular disease-specific mortality.
National and international organizations should consider health as part of their evaluations of the potential benefits and harms of palm oil production and consumption, weighing these against relevant alternatives in light of a growing body of evidence regarding the disproportionate health harms of saturated fat in the context of rapidly developing countries. Currently, the World Bank's Draft Framework for Engagement in the Palm Oil Sector cites "poverty reduction" as a key rationale for supporting palm oil production, citing "negative environmental and social impacts" but not health concerns as potential drawbacks of the strategy . The case of palm oil represents a more general problem that programs focused on economic development and those focused on health are often siloed. As part of the discussion around the United Nation's High-level Meeting on Non-communicable Disease Prevention and Control in September 2011, recent calls have included the development of "healthy crops" and policies that encourage their sustainability  and the deeper involvement of the World Health Organization in food and agricultural production to support these efforts .
Policies that curtail palm oil consumption in rapidly developing countries require careful consideration. One policy now in use to lower CVD risk in developed countries has been to reduce the use of hydrogenated oils, which contain the trans-fats that raise LDL in a similar manner to that of saturated fats. However, in many countries, this has led to substitution of palm oil for trans-fats, which may undermine the health goals of these efforts. Nutritional and environmental concerns associated with palm oil production and consumption may prompt a call for measures to increase the relative price of palm oil. Benefits of such a policy must be weighed against what fat substitutes would be made, especially by poorer individuals, if the prices of both trans-fats and saturated fats were targeted via tax policies.
Our findings are consistent with the extensive literature documenting the link between the consumption of saturated fats (such as palm and coconut oil, as well as animal fats) on plasma total cholesterol and LDL cholesterol and ischemic heart disease [2, 4–6, 8–13]. National and international organizations including the World Health Organization and U.S. Departments of Agriculture and of Health and Human Services recommend consuming fewer saturated fats as opposed to monounsaturated or polyunsaturated fats to reduce the prevalence of cardiovascular diseases [33, 34].
Our findings are also consistent with the previous results that show that high serum LDL levels cause predominantly IHD and some strokes through blockage (thrombosis) in vessels narrowed by atherosclerosis, whereas LDL has no important relationship to hypertension, which can lead to many strokes from hemorrhages of the cerebral blood vessels. Therefore, our finding of a weaker relationship between palm oil and stroke than IHD is consistent with the expected role of higher LDL levels.
The relationship between increased palm oil consumption in developing countries and IHD mortality is consonant with the previously mentioned link between saturated fat consumption and IHD mortality. The weaker relationship between palm oil consumption and IHD mortality in historically high-income countries could be due to a variety of reasons. In many historically high-income countries screening for cardiovascular diseases is more common, the use of drugs such as statins for both primary and secondary prevention is more widespread, and, in general, the quality of hospital care and availability of advanced lifesaving technologies may be better. Additionally, in many historically high-income countries, the proportion of diets that comes from saturated fats is more stable. Also, the lower marginal increases in CVD deaths from increased palm oil consumption in historically high-income countries may be due to the fact that at baseline palm oil consumption levels were already relatively high and saturated fats from animal products remained the major sources of saturated fat for most people's diets.
There are several limitations to this study. First, major palm oil producing and consuming countries including Indonesia and Malaysia were not represented in the present analysis because complete data on other characteristics including cause-specific mortality and cigarette consumption were not available for the time period considered. The relationship of palm oil consumption and health in these settings is of great interest and should be explored when such data become available. Second, cigarette consumption per-capita does not have a statistically significant relationship with cardiovascular mortality outcomes in our analysis. This could potentially be due to collinearity with other variables in the regression. Of note, cigarette smoking is expressed as additional pieces (e.g., cigarettes) consumed per-capita each year. While pack consumption or pack-days are often used, the quantity of cigarettes in a pack changed within countries and over time in our multi-country analysis prompting us to report outcomes in per-cigarette terms to avoid potential confusion as to the definition of packs when the results are interpreted. For example, a common pack size in Australia is 25 although 20-40 cigarette packs are sold. In Canada, it is 20-25, and in Malaysia, a pack can have as few as 14 cigarettes. In fact, in some developing countries, stores often sell individual cigarettes. Third, the use of country-level data in this ecologic study may mask individual variability in the consumption of palm oil and its real impact on health. Importantly, our study employs an econometric model that does not explicitly adjust for all factors that affect CVD deaths. However, by employing country fixed effects that control for time-invariant confounders we partially address omitted variable bias. Our regression results may have a causal interpretation if we assume that unaccounted IHD and stroke risk factors remain constant within each country throughout the study period and no selection biases exist. We also make no cross-sectional comparisons, avoiding selection issues associated with non-randomized samples. However, if palm oil consumption is correlated with other time-varying IHD and stroke risk factors then our analysis cannot separately disentangle the causal impact of palm oil consumption on IHD and stroke from the effects of these other factors. Despite our adjustment for cigarette use and per-capita GDP, the possibility of other unmeasured changes contributing to the effect is real as developing countries have seen nutritional transitions that include increased obesity rates. Our sensitivity analyses suggest that the effect we have estimated for IHD in developing countries is fairly robust with respect to changing patterns of consumption of other major sources of saturated fat, though other factors not included may still play an important role. Nonetheless, ecological estimates that are consistent with smaller randomized trials examining intermediate outcomes and known biological mechanisms contribute significantly to the evidence on important issues like the link between palm oil consumption and CVD mortality.