Cach tinh chi so BMI chinh xac: cong thuc, bang va y nghia ket qua

Chi so khoi co the (BMI) la phep do lien he giua can nang va chieu cao de uoc tinh xem mot nguoi co can nang khoe manh hay khong. Duoc phat trien boi nha toan hoc Bi Adolphe Quetelet vao nam 1832 va duoc WHO chap nhan lam chi so suc khoe tieu chuan.

BMI la cong cu sang loc duoc su dung rong rai nhat tren the gioi boi bac si, chuyen gia dinh duong va co quan y te cong cong. Voi mot con so duy nhat, ban co duoc tham chieu nhanh ve tinh trang dinh duong cua minh.

Tinh BMI ngay lap tuc voi may tinh BMI NexTools, chap nhan ca he met (kg/cm) va he Anh (lb/ft) va hien thi phan loai theo WHO.

Cong thuc BMI la mot trong nhung cong thuc don gian nhat trong y hoc:

BMI = Can nang (kg) / Chieu cao (m)²

Vi du 1 (he met): Nguoi 75 kg cao 1,72 m:

BMI = 75 / (1,72 x 1,72) = 75 / 2,9584 = 25,35

Vi du 2 (he Anh): Nguoi 165 pound cao 5'8" (68 inch):

BMI = (165 / (68 x 68)) x 703 = 25,09

Bang tham khao nhanh (cao 1,70m):

To chuc Y te The gioi (WHO) thiet lap cac phan loai sau cho nguoi lon tren 18 tuoi:

Quan trong: Doi voi nguoi chau A, WHO khuyen nghi nguong khac: thua can tu BMI 23 (thay vi 25) va beo phi tu BMI 27,5 (thay vi 30), vi cac bien chung chuyen hoa xuat hien o gia tri thap hon.

Du lieu 2025: Theo WHO, 39% nguoi lon tren the gioi bi thua can va 13% bi beo phi. Tai Viet Nam, ti le thua can va beo phi o nguoi lon tang nhanh, dat khoang 20%.

Doi voi tre em va thanh thieu nien (2-19 tuoi), BMI khong duoc giai thich bang cung nguong nhu nguoi lon. Thay vao do, su dung phan vi so sanh BMI cua tre voi cac tre khac cung tuoi va gioi tinh:

Tai sao tuoi quan trong: BMI 22 co the hoan toan binh thuong voi nguoi lon nhung cho thay thua can o tre 8 tuoi.

BMI huu ich nhu cong cu sang loc nhung co han che quan trong o cap do ca nhan:

• Khong phan biet co bap va mo: Van dong vien co bap co the co BMI 30+ (phan loai beo phi) trong khi co ti le mo co the thap.
• Khong xet den su phan bo mo: Mo bung (noi tang) nguy hiem hon nhieu so voi mo duoi da o hong va chan.
• Thay doi theo chung toc: Nguoi chau A phat trien van de chuyen hoa o BMI thap hon.
• Khong ap dung cho phu nu mang thai.
• Mat do chinh xac o nguoi cao tuoi: Mat co bap va chieu cao lam sai lech phep tinh.

Cac phep do bo sung chinh xac hon:

• Vong eo: Nguy co tang neu > 102 cm nam hoac > 88 cm nu.
• Ti le eo-hong: Nguy co neu > 0,90 nam hoac > 0,85 nu.
• Ti le mo co the: Do bang phuong phap dien tro sinh hoc, DEXA hoac do nep gap da.

Neu BMI cua ban ngoai pham vi binh thuong (18,5-24,9), day la cac khuyen nghi dua tren bang chung:

Giam BMI (thua can/beo phi):

• Thieu hut calo vua phai: Giam 500 calo moi ngay de giam khoang 0,5 kg moi tuan.
• Hoat dong the chat deu dan: 150 phut hoat dong vua hoac 75 phut hoat dong manh moi tuan (WHO).
• Uu tien protein: 1,2-1,6 g protein moi kg can nang.
• Giac ngu: Ngu duoi 7 gio tang hormone doi (ghrelin).

Tang BMI (thieu can):

• Du thua calo co kiem soat: Tang 300-500 calo moi ngay voi thuc pham giau dinh duong.
• Tap suc manh: De tang can bang co bap, khong chi mo.
• Kham bac si: Thieu can co the chi ra van de hap thu hoac tuyen giap.

Tinh luong calo can thiet voi may tinh TDEE va theo doi tien trinh voi may tinh BMI.

Nhieu nghien cuu dich te hoc xac nhan moi quan he giua BMI ngoai pham vi va tang nguy co benh:

Nguy co cua thua can va beo phi (BMI >= 25):

• Tieu duong type 2 (nguy co cao 3-7 lan voi BMI >= 30)
• Benh tim mach (tang huyet ap, nhoi mau co tim, dot quy)
• Mot so loai ung thu (vu, dai trang, than)
• Ngung tho khi ngu
• Thoai hoa khop

Nguy co cua thieu can (BMI < 18,5):

• He mien dich yeu
• Loang xuong
• Thieu mau va thieu dinh duong
• Van de sinh san

"Nghich ly beo phi": Nghien cuu gan day cho thay nguoi thua can nhe (BMI 25-27) co ti le tu vong tuong tu hoac thap hon nguoi binh thuong. Dieu nay khong co nghia thua can la khoe manh, ma BMI la chi so khong hoan hao.

BMI duoc tao ra nam 1832 boi Adolphe Quetelet, nha thien van hoc va toan hoc Bi. Den nam 1972, nha sinh ly hoc Ancel Keys doi ten thanh "Body Mass Index".

Cac chi so thay the dang noi len:

• BRI (Chi so do tron co the): Dung vong eo va chieu cao. Du doan mo noi tang tot hon BMI.
• BAI (Chi so mo co the): Dung vong hong va chieu cao. Khong can can nang.
• FFMI (Chi so khoi luong khong mo): Dieu chinh cho thanh phan co the. Huu ich cho van dong vien.
• Ti le eo-chieu cao: Don gian va hieu qua. Muc tieu: vong eo nho hon nua chieu cao.

Mac du co han che, BMI van la phep do duoc su dung nhieu nhat nho su don gian. May tinh BMI cho ket qua trong vai giay.