A new study from Finland is adding fuel to the food tribe debate, and protein enthusiasts may not like the headlines this study is generating. Given the popularity of diets skewing higher in protein and lower in carbohydrates, you may find these results surprising. But should this latest diet study persuade you to reconsider your protein intake? Here’s our take.
Researchers examined the impact of self-reported protein intakes of middle-aged and older Finnish men to study the role of dietary proteins and risk of heart failure. This population-based cohort study randomly selected about 2,400 men from eastern Finland and followed them for an average of 22 years, examining their risk for cardiovascular disease-related outcomes. Enrollment and baseline examinations (including one four-day food record) took place between 1984 and 1989. At the end of the study, 334 cases of heart failure were recorded.
What did the study find?
Compared to those eating lower amounts of protein, men who ate more protein were younger, more likely to be married, more educated and had a higher income. However, they were more likely to have diabetes and higher BMIs, and they ate more fiber, polyunsaturated fats, fruits, berries, vegetables and processed red meat.
The participants’ average protein intake was about 90 grams/day or 16 percent of total energy intake, which closely mirrors average U.S. protein intake. Of those 90 grams, 70 percent was from animal sources (mostly dairy, meat and fish), 28 percent came from plant sources (mainly grains and potatoes) and 2 percent was from mixed sources. Interestingly, total protein intake from meat, meat subtypes, milk, fish, eggs and plant sources were not associated with an increased risk for heart failure. In the end, the study found that high total protein intake was “marginally associated” with increased risk of heart failure, teetering on the edge of statistical significance.
In addition to looking at total protein intake, the study also examined associations between heart failure and different animal and plant protein sources. For example, total dairy and fermented dairy protein (e.g., sour milk), but not non-fermented dairy like milk, were associated with increased heart failure risk, particularly among the highest protein consumers. Although the data show a difference in risk, the authors made sure to state that “we did not find a plausible explanation for why fermented dairy or its protein would be more detrimental than non-fermented dairy. Thus, considering that we included many analyses in the present study, we cannot exclude the possibility of a chance finding explaining the result.” These types of findings can occur often in studies with large amounts of data and an arbitrary and sometimes misused threshold to determine if a finding is significant or not.
Where does the study fall short?
Dietary intake was assessed through a single four-day dietary record that was collected in the 1980s. We’ve discussed the utility of such methods in observational research before, as have others. While dietary records can be useful, they’re also a hallmark limitation of nutritional epidemiology studies because short, one-time measurements don’t paint an accurate picture of peoples’ long-term (historical or future) eating patterns. There are many different ways to measure dietary intake, and advancements such as the USDA Automated Multiple-Pass Method have been made since this study’s data collection occurred three decades ago.
In addition, the dietary assessment used for this study was rather simple compared to today’s standards, lacking many categories, which makes the resulting associations less precise. The authors of the study acknowledge these shortcomings: “The single baseline measurement of diet and other lifestyle factors and the inability of a four day food recording to accurately assess typical intakes of occasionally consumed and seasonally varying foods could introduce random error and thus attenuate associations.”
While the study collected records of what people ate, unfortunately, the way people prepared their food wasn’t captured. This is an important omission because certain food preparation methods have been shown to impact health differently. For example, baking or broiling is more heart-healthy than frying. Having more information about the culinary techniques used on the protein foods consumed by these older Finnish men could provide additional insight into their health outcomes.
Speaking of older Finnish men: Because the relatively small sample (for epidemiological research) is limited, it’s impossible to speculate on the applicability of the results, even to their female Finnish counterparts. Unfortunately, media headlines often neglect this tenet of research reporting and translation.
Lastly, a recurring point that we can’t stress enough: By design, observational studies aren’t equipped to determine cause and effect. Thus, they can’t highlight a biological mechanism between any potential relationship—in this case, protein intake and heart failure. They can, however, generate associations and hypotheses for future study in randomized controlled trials where causal relationships can be made. More rigorously designed research looking at this connection is needed.
While this study may be getting attention from the press, it’s not something most nutrition professionals would recommend changing your diet over. This study doesn’t change what we know about the benefits of protein for health, the amount we should consume or the integral role of protein for aging populations.
Dietary protein is an essential nutrient for maintaining muscle strength, bone health and blood sugar control. Protein-rich foods contain many of the vitamins and minerals needed to support body defenses and promote quicker healing. Eating protein-rich foods early in the day can also help you meet and maintain your weight goals by satisfying hunger and reducing the urge to snack between meals. The importance of quality nutrition is even greater as our appetite and calorie needs decrease with age, because preserving our body’s muscle tissue by maintaining protein intake allows us to stay active. Eating enough protein is also associated with reduced risk for bone fractures, an important concern for older adults.
The Recommended Dietary Allowance (RDA) is 54–72 grams of protein per day for a 150- to 200-lb. adult. This is a general guideline to find the minimum amount of protein you need based on your body weight. The best methods for meeting your protein needs are to read food labels and choose foods with at least 5 grams of protein per serving; choose protein sources that are lower in sugar, saturated fat and sodium whenever possible; and distribute your protein intake throughout the day.