>>> we're back with some important health news tonight about diet and its impact on heart disease. there's new evidence about the dangers of sugar drinks and red meat. we get the story from nbc's chief science correspondent robert bazell.
>> reporter: every day we make decisions about what to eat and what to drink.
>> i go through phases of different soda, you know, pepsi, then there's mountain dew.
>> reporter: but what's good for us one day is not the next. that's because research hasn't always been clear.
>> back in the late 1970s people were being told to avoid eggs or a little bit later to avoid all fat if you possibly could. but there was actually no evidence, no data supporting that.
>> reporter: now, long-term research is steadily revealing that little decisions we make actually carry a lot of weight. in a new study, researchers at harvard university followed more than 40,000 men over 22 years and found that those consuming just one 12-ounce sugared sweetened drink a day increased their chance of having a heart attack by 20%. two sugary drinks, 42% increase and three a day, 69%.
>> it does cause a spike in blood sugar and causes a big burst of insulin. if we do this day after day, that's hanging around. that's not just a spike for a few hours.
>> reporter: the american beverage association disagrees and in a response to the study said drinking sweetened beverages does not cause an increased risk of heart disease. adding these findings, quote, could have been the result of other lifestyle changes. another study looking at red meat consumption over 28 years found men and women who ate a serving a day were 13% more likely to die prematurely. the national cattleman's beef association says no one food has quote been shone to affect mortality. and the scientific evidence to support the role of lean beef in a healthy balanced diet is strong. the results from many students accumulate, what defines a healthy diet is becoming ever more clear. experts suggest eating less red meat and more nuts, poultry and fish as sources of protein. eating fewer refined carbs and staying away from trans fats and going for good fats instead. we know what's good for us and what's not.
>> makes me kind of not want to eat it as much. but i probably still will.
>> reporter: the real question is do we have the will power to make those healthy choices? robert bazell, nbc news, new
