Putting Diets to the Test

As a new year begins, it will be hard to avoid diet propaganda. I call it propaganda because in my review of the weight loss literature, I find very little evidence that diets are effective for the majority of people who try them. [In contrast, adopting a certain diet pattern (e.g., Mediterranean or plant based) as a life style is health promoting.] 

In some ways, diets are like medication and this may explain why diets fail.  First, like hypertension medication, diets work as long as you ‘take’ them and few diets are palatable or tolerable enough to 'take' forever. Second, like medication for serious mental illnesses, the side effects may be so harsh that the people who need the medicine most cannot tolerate it; like a diet which causes an excess amount of flatulence.  Third, the medication regimen may feel more tedious than the immediate or future disease complications seems to warrant; like drinking vinegar after every meal. Lastly, like pain medications, diets may need tweaking in order to remain effective; once weight is lost, a person requires fewer calories to maintain the new weight.  

Diets are not medications however; they are behavioral modifications or interventions. Considering the above analogies, a successful behavioral intervention for weight loss is as much dependent on the person as it is the intervention. To be successful, the intervention/diet needs to be one that a person is able to follow (with occasional adjustment) without mental or physical anguish for their entire life.  A person could not return to unrestrained eating or reduce their level of physical activity and expect the benefit of said diet to continue.  

Another important factor regarding diets is the amount of weight loss necessary for an individual or sponsor (e.g., government, worksite, researcher) to consider the diet ‘successful.’ Scholars Tomiyama, Ahlstrom and Mann recently raised this issue in an article they wrote for the journal Frontiers in Psychology.  In their article, they suggest holding behavioral interventions, including diets, to the same standards of evidential effect as medications (i.e., FDA approval).  Recall that a drug company has to proceed through certain steps when requesting a new drug application.  It has to show a drug:

• is safe, usually done first in animal studies 
• has limited side effects (ones that are outweighed by the benefit of the medicine)
• addresses an issue or disease that significantly impairs health or quality of life
•  is better than an existing drug for this particular disease 

•  the new drug has to be more effective, have less severe side effects or both  
•  or the regimen for the new drug has to be easier to tolerate than the current treatment (e.g., a once a month injection for osteoporosis treatment vs a daily or weekly pill taken on an empty stomach) 

Drug companies usually start a drug application with the intention of treating only one disease, but they must identify the disease.  Testing goes from the lab, to small groups, to large clinical trials, and then to post market evaluation. 

Imagine the same process for a diet intervention and include efficacy and effectiveness markers, as Tomiyama and colleagues suggest.  A diet intervention (or drug) is efficacious when it works in a lab under controlled conditions and effective when it works in the real world under less than ideal situations –where people might not follow every instruction, every time.  This is where diets seem to fail the most.

Tomiyama and colleagues give a thorough commentary on using FDA standards to test behavioral interventions and they use obesity as their example.  I was able to access the full article after clicking this link and then the tab on the right that says ‘provisional pdf.’ If this idea (testing interventions with the same rigor as testing new medications) intrigues you, I strongly recommend you read the original article.  

My last thought regards something the authors did not mention in comparison to drug trials, but which I would add – marketing and labeling.  A drug company can only market a drug to treat the condition tested in clinical trials.  In addition, marketing material and product labels must include information on side effects; instruct people how to take the drug, and state that not everyone will have the same benefit or side effects when using it.  I would be happy to see this sort of disclosure with diet programs, and expect that if such a high standard were required, most diets would fail to reach ‘market.’

Instead of trying a diet program or worse, diet supplement you see advertised in the coming weeks, why not read more about a health promoting pattern of eating from Harvard’s Nutrition Source – here.

Tomiyama A, Ahlstrom B and Mann T (2013). Evaluating eating behavior treatments by FDA standards. Front. Psychol. 4:1009. doi: 10.3389/fpsyg.2013.01009