While many adults struggle with restrictive dieting and counting calories, Harvard University researchers found that the type of foods we choose to eat may have a bigger impact on weight control than portion sizes.
More from TODAY.com
Hillary Clinton: Granddaughter led me 'to speed up' political plans
Clinton said she is inspired to keep working to ensure that Charlotte and her generation are provided equal opportunities ...
- Lauren Hill, inspirational college basketball player, dies
- Marathon dad's victories help raise money for son with spina bifida
- Will it work on Vale? Savannah tries tissue sleeping trick at home
- Listen to the chilling 911 call Sandra Bullock made during break-in
- Hillary Clinton: Granddaughter led me 'to speed up' political plans
Regular consumption of potato chips, French fries and sugared beverages were most to blame for slow and steady weight gain. However, people who ate yogurt, fruits, vegetables, nuts and whole grains either lost weight or gained the least.
The researchers analyzed data on three separate studies over a 20-year period, tracking the long-term effects of different foods and lifestyle changes on more than 120,000 men and women. Adults in the study gained an average of 3.35 pounds every four years, for a total average weight gain of almost 17 pounds.
Dr. Walter C. Willett, chairman of the nutrition department at the Harvard School of Public Health discusses the implications of the study.
This interview has been edited for length.
Q. What's the main message about the study on different foods and their effect on long-term weight gain?
A.The important point of this study is that there’s no magic bullet ... that we really need to pay much attention to the quality of [our] diet. Picking out healthier foods, fruits, vegetables, nuts, whole grains, each one of these will have a small benefit. But adding them all up, it’ll make a long-term difference in our long-term ability to control our weight.
The bottom line here is, the quality of the diet can make a big difference in the long-term ability to control our weight. And that, of course, has many implications for our long-term health and well-being.
Q. What is the biggest bill on American diets?
A. Sugary beverages -- sodas, sports drinks -- were among the top contributors to weight gain. They are a special problem because so many people consume multiple servings of sugary beverages on every day. That makes them the number one problem related to weight gain.
But, still, the message here is that there is no one single villain or one single solution to weight gain. It is really the combination of multiple contributors in the diet.
Q.The study shows that eating potato chips cause weight gain and yogurt tends to [lead to] weight loss. Can you explain why you don't worry about portions? If you ate a bucket of yogurt and one potato chip, clearly, they would have different effects on your body.
A. Certainly, paying attention to portions sizes makes sense. But, also, it is pretty clear that the kinds of foods we eat make it harder or more difficult to control our caloric intake.
Some foods like potatoes, we eat in a cooked state and we digest those foods very quickly. They turn to blood sugar very rapidly ... and they don’t leave us satisfied for a long period of time. On the other hand, something like an apple is digested very slowly. We chew it quite a bit; that slows us down. Then, the stomach takes some time to break apart the cells in an apple. The sugar and starch from an apple is released very slowly into the blood stream. There is a lot of fiber there that keeps our stomach fuller for a long time and that makes us less hungry one or two or three hours down the road than the potato.
As it turns out, the foods that make it easier to control our calories in the long run are the same sets of foods that we seem related to better health or lower risks of diabetes or lower risks of heart attacks.Story: Weight Watchers, DASH diets best, researchers say
Q. Yogurt is considered a healthy food, but people who eat it also seem to do better with weight. Could that be a marker for better, healthier lifestyle, or is it something about yogurt?
A. Yogurt was sort of a surprise here. It did come out in all three of the studies that we looked at, that are a part of this report. The yogurt finding does need to be looked at in further detail.
There has been some recent information suggesting that the changes in the bacteria that live in the colon may be important in controlling weight, as well. So, this is a promising lead.
Q. Let’s take the worst of the study: potato chips. Do more people who tend to eat potato chips tend to be junk food eaters in general, or is it that potato chips tend to be practically bad?
A. On average, people who ate more potato chips tended to eat other unhealthy things in the diet. But we looked at that pretty carefully and adjusted for those other factors -- and, still, potato chips held up on their own.
Maybe you’ve heard the line that 'you can’t stop after eating just one,' and that’s part of the problem with potato chips.
Q. And it seems orange juice is not that much better in terms of weight control than sugared beverages. There’s this whole idea that juices are healthy. How do you deal with that in terms of public health recommendations?
A. People have been given the idea that fruit juices are a really healthy choice, but, in fact, fruit juice has just about the same number of calories as a full-sugar soda. And it’s just as easy to over-consume fruit juice just as it is to over-consume regular soda.
Also, we’ve seen that fruit juice is related to a higher risk of diabetes, just like soda is as well. Fruit juice is fine -- maybe a small glass once a day, but definitely not a good idea to consume it like a regular beverage.
Q. Peanuts and other nuts did fairly well. Why is that? They’re a very calorie-rich food.
A. In this study, and many other studies, it has been found that tree nuts and peanuts as well are not related to higher weight gain. Nuts are very satisfying; calorie-for-calorie we’re less likely to be hungry three or four hours down the road than if we were eating some other type of food. In the long run, it can add up to less weight gain.
Q. This study will be seen mostly about types of foods that affect weight gain, but I presume this is because you controlled for the exercise and the other life style factors?
A. We found that more [exercise] was related to less weight gain. We also looked at television and watching TV was related to more weight gain.
Q. How can this study reflect in public policy?
A. Individuals ultimately decide what they put in their mouths, but there are many things in our environment that make it more difficult to get healthier foods. Many people in urban areas and some rural areas don’t have very good access to healthy food on a regular basis and we need policies that can change that.Story: America's bad eating habits get even worse
Also, what we make available in school cafeterias and work sites has a big impact on what people eat. We can help people make healthier choices; there’s a lot we can do.
© 2013 NBCNews.com Reprints