Derived mostly from fish oil, these compounds have been trumpeted as being protective against many cardiovascular and other diseases, so are widely sold. However, clinical trials have not shown consistent evidence of benefit and the NATIONAL INSTITUTE FOR HEALTH AND CARE EXCELLENCE (NICE), while advising that people with or at high risk of heart disease should consume at least 2 portions of fish per week including a portion of oily fish, also states that omega-3 fatty acid compounds should not be offered for primary or secondary prevention and that healthcare professionals should tell people that there is no evidence that omega-3 fatty acid compounds help to prevent heart disease. To the contrary a trial from the US, reported in 2016, suggested that high dose omega-3 fatty acids do improve heart muscle function and reduce heart muscle scarring after a myocardial infarction. Also, dietary deficiency in pregnancy and during breast-feeding may be harmful to a baby's developing brain, so women of childbearing age are advised to eat 1–2 portions of oily fish (e.g. mackerel, sardines) weekly – but not more, because of concerns about heavy metal and dioxin contamination of some fish.