Is read meat a deadly poison?
Recently a new report has been published from the famous Channing Laboratory at Harvard. Here, a number of researchers headed by Walter Willett have studied the dietary habits for many years in more than 100,000 men and women. Again and again they have warned us against saturated fat, although none of their many studies have found that heart patients have eaten more of such fat than have other people. However, as I told you in my December Newsletter Willett has changed his mind
This time the message, published in Archives of Internal Medicine, is that you will shorten your life if you eat too much unprocessed read meat. Two population groups, the Health Professionals Study that included 37698 men, and the Nurses’ Health Study that included 83644 women, were followed for 22 and 28 years, respectively. At the start and every 4 year they filled in a dietary questionnaire.
At follow-up almost 24,000 had died. The authors divided the participants into five parts (quintiles) after their intake of read meat. The first quintile included those who had eaten the least, and the fifth those who had eaten the most. From the figures in the tables it is possible to calculate the mortality in each group.
The pattern was similar in both groups, but for simplicity I give you the figures for the Health Professionals´ Study only. Here 1.23 per cent had died each year in the first quintile; and 1.29 per cent in the fifth quintile. Thus, during the 22 years the total mortality in these two groups was 27.1 and 28.4 per cent, respectively.
But it was only 21.8 per cent in the third quintile! So, what shall we do? If we eat too much, the risk increases, but so it does if we eat too little. How can we know whether we eat too much or too little?
However, there were many factors that could have skewed the result. For instance, those with the lowest intake were more physically active, fewer smoked, they ate more fruits, vegetables and fish, and fewer had diabetes and high blood pressure compared with the other groups. These life style factors were particularly bad in the fifth quintile.
But as mentioned, the risk of dying was about the same in all groups. You could also say that even if you smoke, eat too little fruits, vegetables and fish, and even if you have diabetes or high blood pressure, then you may live almost as long as people with a healthier lifestyle if you gorge in unprocessed read meat.
The authors concluded otherwise, however, because their statistician has made some serious errors. After having corrected for the uneven distribution of the various factors, they found that the risk of dying was lowest in the first quintile and it increased step by step from the first to the fifth quintile. Their conclusion was that if you consume less than 42 gram unprocessed meat per day, you could lower your risk to die the next 22-28 years by about 8 per cent.
It is not possible to know the exact mortality after their corrections, because it is expressed in a statistical term called hazard risk. But let us assume that the risk after the corrections was 30 per cent for those with the highest intake and 27.6 per cent for those with the lowest. These figures are of a similar magnitude as those that we can calculate ourselves from the original figures. The difference between 30 and 27.6 is 2.4, meaning that you can only lower your risk of dying by 2.4 per cent. Then how can they conclude that we can lower it by 8 per cent? Because 2.4 is 8 per cent of 30.
There are more curious data. The body weight of the participants was pretty normal in all groups. To be precise, their BMI varied between 24.7 and 26.0. But whereas the high-consumers on average ate about 2200 calories per day, the low-consumers ate only 1659. In the Nurses’ Health Study, where BMI varied between 23.9 and 24.7 the high-consumers ate 2030 calories and the low-consumers only only 1202! These figures are of course highly unlikely. People who have eaten only 1202 calories per day for 28 years cannot have the same body weight as people who have eaten 2030 calories per day.
Thus, the statistician must have made some serious miscalculations. But let us assume that the figures are correct. Should we really bother? Let me calculate it in another way.
If you eat as much unprocessed read meat as you like, your chance to be alive after 22 years is about 70 per cent, but if you avoid it as much as possible you can increase your chance to 73 per cent at most. But again, this is true only if the data published by Hu and his coworkers are correct, and this is very unlikely.
You can learn more about this paper by reading a detailed comment by one of our members Zoë Harcombe. She also asked Frank Hu, if he could explain the curious result. Here is his answer:
Thanks for your interest in our paper. Unfortunately, the crude mortality rate is misleading because the mean age in the first quintile (Q1) was older than other quintiles. Therefore, the crude mortality rate in the first quintile would be artificially higher than other quintiles. In this analysis, age was a stronger confounding factor than other lifestyle factors.
Hope this helps.
This answer is nonsense, because there were only minor differences in age between the five quintiles. In HPFS it varied between 52.2 and 53.8, and in NHS between 45.3 and 47.3 years. For instance, compare these small differences with the fact that in the fifth quintile there were almost three times more smokers than in the first; and only 17 percent were physically active against 27 percent in the first.
Professor David Diamond, another member of THINCS, sent him a letter as well, but hitherto Frank Hu hasn´t answered him.
Do you become fat by eating fat?
A last question: Do you suffer from obesity? Then listen to this brilliant lecture by Zoë Harcombe.