“深海魚”多吃有益?! 還是少吃為妙?! <二>

上期談及多吃深海魚的益處，但我們往往會因深海魚的水銀含量高而卻步，那我們應如何選擇深海魚及究竟吃多少才能獲得其好處，又可避免攝取過量水銀呢? 以下『紅綠燈』可供各位精明消費者在選購深海魚時作參考。

表一: 選魚『紅綠燈』

『紅』燈	『綠』燈
劍魚	三文魚
鯊魚	沙甸魚
馬頭魚 / 方頭魚	鯖魚(大西洋)
旗魚	鰈魚
大眼吞拿魚	鱈魚 (pollock)
藍鰭吞拿魚	虹鱒魚
大鯖魚 /鮫魚	鯡魚
資料來源: 食物安全中心、美國食物及藥物管理局、加拿大卑詩省衛生廳

魚類中的水銀含量，視乎其品種、年齡、覓食模式和生活水域而定。壽命越長或在食物鏈的位置越高的魚類(如體型較大的捕獵魚類)，體內積聚的水銀就會越多。

上述『紅』燈組別的魚，總水銀含量平均值較高(表二)，因此不宜經常食用。聯合國糧食及農業組織 / 世界衞生組織聯合食品添加劑專家委員會於二零零三年訂定水銀的安全攝入量，即暫定每周可容忍攝入量為每公斤體重1.6微克。以體重60公斤的成年人為例，一周內吃3安士(85克, 約一隻掌心大小)馬頭魚，已超出容忍攝取量的30%。而由於水銀對孕婦、計劃懷孕的婦女和幼童的影響較大，所以應避免選吃此類水銀含量可能較高的魚類。

『綠』燈組別的魚，總水銀含量平均值較低(表二)，可適量進食多種魚類。美國心臟學會便建議成人每周進食2至3次，每次3安士的深海魚，便可滿足一周所需。不同年齡組別之奧米加-3的建議攝取量見表三。

表二: 各種魚類之平均總水銀及奧米加-3含量

種類	平均總水銀含量 (微克/公斤, μg/kg)	奧米加-3含量 (克/3安士)
總水銀含量平均值偏高的魚類
劍魚	970 – 1820	0.97
鯊魚	540 - 1500	0.83
馬頭魚 / 方頭魚	1450	0.90
旗魚	1100 – 1430
大眼吞拿魚	639 - 740	1.36
藍鰭吞拿魚	730	1.17 – 1.50
大鯖魚 /鮫魚	730	0.36
總水銀含量平均值較低的魚類
三文魚	10	1.10 – 1.90
沙甸魚	13	1.30 – 2.00
鯖魚(大西洋)	50	1.10 – 1.70
鰈魚	50	0.48
鱈魚 (pollock)	60	0.45
虹鱒魚	70	0.84 – 0.98
鯡魚	80	1.70
資料來源: 食物安全中心、美國食物及藥物管理局、美國心臟學會

Deep sea fish- harmful or helpful? Part 2

We talked about the pros of eating deep sea fish in the last issue, but we often avoid deep sea fish due to its mercury level.  So how should we choose which deep sea fish, and how much should we eat, as to benefit from its advantages without intaking excessive mercury?  The chart below can serve as reference for every smart consumer when choosing deep sea fish.

Chart 1: fish traffic light

Red light	Green light
Swordfish	Salmon
Shark	Sardine
Tilefish	Atlantic Mackerel
Sailfish	Flounder
Big-eye tuna	Pollock
Bluefin tuna	Rainbow trout
King mackerel	Herring
Source: Hong Kong Centre for Food Safety, US FDA, British Columbia Ministry of Health

The mercury level in fish depends on its species, age, foraging mode and habitat.  Those which are older or placed in higher position of the food chain (fish larger in volume) contains more mercury in their body.

Those listed in the ‘red light’ column are fish that contains higher average mercury level (chart 2), and should not be frequently consumed. The maximum safe intake level of mercury, set by the Food and Agriculture Organization of the United Nations and the WHO Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2003, was set at 1.6 microgram per kg weight per week.  For example, if an adult of 60kg weight intake 3ounces (85g, size of a palm) tilefish, the mercury level already exceed the maximum safe level by 30%.  As the impact of mercury is particularly susceptible to pregnant women, women preparing for pregnancy and infants, people falling in these groups should avoid eating fish that might contain high level of mercury.

Fish listed in the ‘green light’ column are those with lower average mercury level (chart 2), and can be consumed regularly.  The American Heart Association recommend weekly intake of deep sea fish for 2-3 times, 3 ounces each.  The recommended intake level of omega-3 of different age groups can be found in chart 3.

Chart 2: average mercury level and omega-3 level of different fish

Species	Average mercury level (μg/kg)	Omega-3 level (gram/3 ounces)
Fish with high mercury level
Swordfish	970 – 1820	0.97
Shark	540 - 1500	0.83
Tilefish	1450	0.90
Sailfish	1100 – 1430
Big-eye tuna	639 - 740	1.36
Bluefin tuna	730	1.17 – 1.50
King mackerel	730	0.36
Fish with lower mercury level
Salmon	10	1.10 – 1.90
Sardine	13	1.30 – 2.00
Atlantic mackerel	50	1.10 – 1.70
Flounder	50	0.48
Pollock	60	0.45
Rainbow trout	70	0.84 – 0.98
Herring	80	1.70
Source: Hong Kong Centre for Food Safety, US FDA, American Heart Association