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Macronutrient Intake Recommendations: What Does the Evidence Indicate?

ScientificJournalWith the increased interest in how we address obesity and the associated metabolic risk factors, there has been more focus on greater understanding of how macronutrient intake (source and amount) affects our health. A big splash occurred with the re-issuing of Atkins’ Diet over a decade ago. Since then, and with the ever-increasing impact of social media, societal interest in how food impacts health has exponentially escalated.

Currently, there are discussions surrounding:

  1. Whether calories are as important to health outcomes as we once thought
  2. The “toxicity” of certain ingredients and nutrients
  3. How the source and type of macronutrient influences our bodies and environment
  4. How genetic alterations of our plant-derived food impacts our health

From a scientific perspective, much of the recent evidence has illustrated how poorly many of the issues are understood, especially when it comes to applying the evidence to individuals and/or populations. For example, recent studies have illustrated that those who increase their intakes of certain foods are likely to gain more weight over time—yet, there was no indication if there was an increased risk for deleterious heart, metabolic, or cancer-related outcomes (Mozaffarian et al., 2011).

A more recent study indicated that increased protein intake did not affect health outcomes when compared with a decreased protein intake. Yet increased protein intake (or decreased carbohydrate intake) has been recommended to reduce the risk for negative cardiovascular events (Schwingshackl and Hoffman, 2013). With the data taken together, there still does not appear to be a population-wide “optimal” macronutrient or food recommendation for health. However, there are ample data that show that DASH (dietary approaches to stop hypertension), Mediterranean, low carb, ancestral or Paleo, USDA recommendations (e.g., MyPlate), and vegan diets elicit significant positive health outcomes. The difficulty is coming to agreement, as there tends to be disagreement about how the outcomes are determined and valued.

One issue that seems to complicate how diet data are interpreted is confirmation bias. This bias has presented itself when issues pertaining to sugar have been discussed. If a study does not agree with one’s perspective, it is dismissed and omitted while another that does support a preferred view is used to explain how sugar affects health.

As an educator, I try to emphasize focusing on the methods and results sections of a study; however, this can be difficult if the methods are not familiar. By eliminating influence by the authors, one might be able to get a truer sense of how the intervention impacted the independent variables. It seems the convenient means of gathering information is to read headlines and non-scientific summaries of the study with quotes from the authors. This approach does not provide the reader with any unbiased information since the methods and data are either not provided or only select aspects of each are presented.

What we, as scientists, need to do is take the time to go to the source to understand the methods and really study the results to conceptualize the outcomes. Try to educate yourself about the research question being addressed instead of relying on an interpretation from others. If the science is outside your area of expertise, reading views from several perspectives might be a better means of unveiling where the truth lies instead of accepting the message from one voice.

Mark HaubMark Haub, PhD
Associate Professor
Dept. of Human Nutrition
206 Justin Hall
Kansas State University

Reference List
Mozaffarian, D., Hao T., Rimm E.B., Willett, W.C., and Hu, F.B. 2011. Changes in diet and lifestyle and long-term weight gain in women and men. New Engl. J. Med. 364: 2392-2404.

Schwingshackl, L., and Hoffmann, G., 2013. Long-term effects of low-fat diets either low or high in protein on cardiovascular and metabolic risk factors: a systematic review and meta-analysis. Nutr. J. 12:48.

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