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Hailing from the US, she has a background in fisheries science and nutrition and thinks of fish consumption from a global perspective. She is also director of the World Health Organisation (WHO) Collaborating Centre for Human Nutrition at Otago.
However, appointed to the university just as the pandemic was starting, she has not been able to come to Dunedin yet and is working from Atlanta, Georgia. Now the borders have opened she plans to move here in time to conduct her lectures in person from the second semester.
"If we speak very generally, fish are a good source of long-chain fatty acids, the polyunsaturated fatty acids that are important for the membranes and our nerve endings and a lot of cell signalling," she said.
Most people are aware there are good fats (mono and polyunsaturated) and bad fats (saturated and trans fats) and that fish in general have good fats, especially omega 3 and omega 6 long-chain fatty acids.
Fish is also a great source of lean protein, she says.
Whereas here we mostly eat filleted fish (apart from whitebait and shellfish), in many traditional societies they eat whole small fish, or parts of larger fish that we generally discard, such as fish heads and livers which are nutrient-dense.
While working with indigenous communities in Alaska, she first came across people who enjoyed eating fish eyeballs. It made her think how they were a unique source of vitamin A, she said.
When she was working in western Kenya around Lake Victoria, she found that larger fish were sent to fancy restaurants or exported but the locals ate omena, small fish about the size of our whitebait.
"If you are eating small fish you are consuming their intestines and their skeletal structure. What is important about those organ systems is you are getting a lot of micronutrients. In food-insecure populations there are often micronutrient deficiencies," she said.
"These small fish are not expensive, they are palatable, they are used in a lot of the local cuisine, which includes fish stews. It’s one of the most nutrient-dense foods available to locals. They are a really important source of proteins, fats and multiple micronutrients that are often absent from the diet."
Many of the health benefits of eating fish (contributing to heart, brain and eye health, and helping prevent depression) come from the long-chain polyunsaturated fatty acids as well as micronutrients, but it depends on how you cook it, she said.
You can reduce the health benefits quickly if you eat your fish deep-fried — such as in fish and chips — rather than steamed or in a stew.
Canned fish has a similar nutritional value to cooked fish.
"Anytime I have the option of fish versus other meats I opt for fish," she said.
She prefers not to talk about the benefits of wild versus farmed fish because of the politics and economics around fish farming, but it depended a lot on what they are fed, Dr Williams says.
You are what you eat and that’s true whether you are buying pasture-raised eggs at the supermarket, or grass-fed dairy or wild versus farmed fish, she explains.
But there are downsides to eating fish, and it’s worth choosing your fish carefully, she says.
With wild fish there is always the issue of sustainability and overfishing, whether a species is endangered and how it is caught.
New Zealand has a quota management system that has both advocates and critics, and Dr Williams points to the example of the International Pacific Halibut Commission with which she has worked. It has the reputation of being one of the best-managed fisheries in the world, she says.
Halibut is a large flat fish caught off the Pacific coast of North America, but almost 100 years ago fishermen realised the population was declining and asked for an oversight. A treaty between the US and Canada established the commission which still manages the fishery, assessing fish stocks and undertaking research.
In general wild-caught fish have been shown to have a lower carbon footprint than lamb or beef, despite the fuel used in boats to catch fish and the processing costs. However, if imported, fish also has the additional carbon cost of the transport.
Then there’s the issue of environmental toxins such as methylmercury, a highly toxic compound in the oceans which can build up in fish, especially in larger, longer-lived species.
Pregnant and lactating women and young children are more vulnerable to the potential toxicity of heavy metals, although they too benefit from the micronutrient density and favourable fatty and amino acids, Dr Williams says.
"If you are concerned about any environmental toxins, you would be interested in eating lower on the food chain. Heavy metals and pollutants have had less of an opportunity to amplify in the smaller fish that are eaten by the larger fish and the fish that have longer life-spans that are big and old and have opportunity to acquire more and more toxins over their lifespan."
A more recently recognised concern is the problem of microplastics in the ocean which fish eat or absorb — but that’s another story.