Nutrition

What’s the best way to cook veges and how many brazil nuts are too many?

What’s the best way to cook veges, and how many brazil nuts are too many?

Question:

For years I’ve cooked my vegetables in a metal slotted steamer over boiling water. I had the idea that steaming was healthier than putting vegetables directly into boiling water. Is this true?

Overboiled cabbage is the stuff of kids’ nightmares. But before we throw the cabbage out with the cooking water, is boiling vegetables really that much worse than steaming them? Vegetables are a readily available source of dietary fibre, vitamins, minerals, phytochemicals that function as antioxidants, phytoestrogens and anti-inflammatory agents and benefit our health in many ways. So, when eating vegetables, we clearly want to absorb as many of those nutrients as possible.

The fibre and fat-soluble vitamins in vegetables, such as vitamin A and E, generally aren’t greatly affected by boiling or steaming. The bioavailability of some nutrients, such as the lycopene found in tomatoes and the beta-carotene in carrots, may actually improve with cooking.

However, vegetables also contain water-soluble vitamins and phytochemicals. And it’s these nutrients that are readily lost through leeching when vegetables are boiled.

Chinese researchers studied the effect on the nutrient content of broccoli of steaming, microwaving, boiling, stir-frying, and stir-frying followed by boiling. They found all cooking treatments, except steaming, caused significant vitamin C losses. Steaming also reduced losses of glucosinolates – the sulphur-containing compounds found in broccoli that are credited with protecting us from cancer and cardiovascular disease.

So, yes, steaming is preferable to boiling for retaining nutrients. However, many variables can affect cooked vegetables’ nutrient content, including cooking time, the amount of water used, how the vegetables are cut and their type.

However you cook your veges, keep them as intact as possible, and if you’re boiling or microwaving them, use as little water as possible.

Question:

I’ve been eating three to four brazil nuts a day for many years. After reading your column on selenium (“Strike a balance”, June 30), I’m wondering how much danger I’ve put myself in regarding type 2 diabetes?

Answer:

A couple of the nuts a day is a tasty and effective source of selenium. They’re the equivalent of a 100-microgram (mcg) supplement, according to

University of

Otagoresearch. But as explained in my earlier column, higher-dose selenium supplements have been linked to an increased risk of type 2 diabetes.

The connection was noted in the Nutritional Prevention of Cancer

However you cook your veges, keep them as intact as possible and go easy on the water.

(NPC) trial in participants who were supplementing their intake of the mineral with 200mcg of selenium yeast a day. Another study, the Selenium and Vitamin E Cancer Prevention Trial (Select), in which participants took 200mcg a day of selenomethionine, also showed up a trend towards higher levels of type 2 diabetes.

Researchers are trying to understand

why. Does the increased risk apply only to certain forms of selenium supplements? Or only to people with higher baseline selenium levels before starting selenium supplementation?

The latter seems possible given that we know there is a U-shaped relationship between selenium and health risk; that is, too little and too much of it is bad for us.

You differ from the people in the study groups in several ways. For a start, you’re getting selenium in the form of food rather than dietary supplements, and you’re probably consuming less of the mineral – three nuts equate to about 150mcg of selenium – than they are.

Also, since New Zealand soils are selenium-poor, without the nuts you’re likely to be getting an inadequate amount of dietary selenium. And the diabetes risk seems greater for males, which gives you another let-off, since I assume from your name that you’re a female.

The recommended daily intake of selenium is 400mcg. Above that, unwanted side effects are possible. To be on the safe side, however, I’d limit myself to two brazil nuts a day.

Email your nutrition questions to nutrition@listener.co.nz