How to Evaluate Diets and Supplements

“This diet helped me lose 25 lbs in 4 weeks!”

“This supplement gave me 150% more energy after just 3 days of taking it!”

“Improve your blood sugars FAST with this new superfood discovery!”

Everywhere you turn, there is some sort of diet or supplement that promises the moon and stars. Some of these messages are especially loud, thanks to their passionate and vocal followers. The inundation of viewpoints leaves you with your head spinning. Throw diabetes management into that equation, and you’re in for quite a challenge.

Sound familiar? Here are some simple tips for distinguishing between sensationalist marketing and science-based diets. But first, know that no single diet works for every single individual. A low-carbohydrate diet may benefit one individual’s A1c and weight loss goals, while a high-carbohydrate diet works for someone else. Also, keep in mind that the loudest voices are not necessarily the most trustworthy. Some diets simply have more passionate followers.

1. Scrutinize the promises of the diet or food.

Do they seem reasonable? Do they raise any red flags? For example, does the advocate promise a weight loss of 30 pounds in one month or that avoiding a particular nutrient is the only way to ensure you won’t get (fill-in-the-blank) disease? As the old adage goes, if it seems too good to be true, it probably is. If it seems too extreme to be true, it also probably is (looking at you, grapefruit diet).

2. Consider the scientific rationale of said diet or supplement.

Most advertisers know that scientific rationale significantly increases the credibility of their claims, so they will provide references and sources. It’s your job to read—or at least quickly review—some of them. Consider the following:

Who funded the study: If the funding is from a public source (i.e. National Institute of Health) and is university-sponsored, the study is more likely to be objectively run than a study that is funded by a company. It’s no surprise that Gatorade was shown to be more effective than water during a workout in a study conducted by the Gatorade Sports Science Institute. Beware of these sorts of studies.

Study design techniques: Most studies will involve a randomized controlled trial (RCT), in which a group of subjects receive an intervention (i.e. a diet pattern or a supplement) and another group, called the control group, receives nothing. If there were no control group to a study, how would the researchers be able to compare the subjects in the intervention to those who are not? Additionally, if it is a supplement study, the participants should be blinded (they should not know if they are receiving the supplement or not), since this knowledge could influence results.

Sample size, population, and adherence: The key here is generalizability, which is the ability to extrapolate results to a larger population. The greater the number of people in a study, the more statistical power there is to show the results did not happen by chance, increasing the generalizability of the research findings.

Additionally, generalizability can be determined in part by the population. If a dietary intervention occurred in middle-aged, obese women, it may be more difficult to translate those results to college-aged, normal weight males. Finally, adherence is important for dietary interventions. This can be noted in a drop out rate – for example, if 78% of participants successfully followed the diet for 12 weeks, that means one out of four people did not. If the study went for a longer period of time, would more people have dropped out?

3. Proceed with caution if only testimonials are offered.

Testimonials can seal the deal, as they offer further evidence of the greatness of a diet or supplement. But if there are only testimonials (no evidence-based rationale), you should be careful, because many advertisers and paid spokespersons will tell you anything to increase profits.

Putting it all together: the ketogenic diet

The ketogenic diet is a prime example of a diet that has been polarizing the diabetes sphere for quite some time. Its staunch believers speak of its ability to reduce blood sugar spikes, while its opponents discuss the difficulty in adherence and falsely claim that the diet results in diabetic ketoacidosis (DKA).

The reality? The ketones produced via the ketogenic diet never reach dangerous, DKA levels, as long as insulin is taken. And while it may help to moderate blood glucose levels, it is not the only diet to do so. Even higher carbohydrate diets can reduce blood sugar spikes. (For a fuller analysis of this particular diet, read my recent post at Diabetes Strong.)

It can be difficult to separate myth from fact, and sensationalism sells. Use the techniques offered here to more critically read and research nutrition and diets.

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Ben Tzeel is a Certified Strength and Conditioning Specialist (CSCS) through the National Strength and Conditioning Association. He is currently attending the University of North Carolina at Chapel Hill, finishing his Master’s Degree in Nutrition and becoming a Registered Dietitian. Ben has lived with Type 1 Diabetes since 1999 and has never allowed it to hold him back from achieving his goals. He is a published fitness model and contributes content about exercise and nutrition to many websites, including Beyond Type 1 and Diabetes Strong, where he is the Fitness Editor. He offers personalized online fitness and nutrition coaching to motivated clients. Reach out to him at or on Instagram at @manoftzeel.

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