Popular fad diets can pack a nutritional punch, new study reveals

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In a recently published study, Dr nutrientsResearchers identified the most “popular” fad dietary patterns in the United States (USA), assessed their diet quality according to the Dietary Guidelines for Americans (DGA), and presented opportunities to maximize their nutritional quality.

Healthy food bowl
Study: An opportunity to maximize the dietary quality of fad diets. Image credit: Creative Cat Studio/Shutterstock.com


Research suggests that most Americans follow a westernized diet high in saturated and trans fats, sodium, sugar, and calories. Americans overconsume refined grains, animal proteins, and alcoholic beverages.

Furthermore, about 80% of Americans generally consume less fruits, vegetables, and fiber than recommended by the DGA.

Simply put, despite concerted policy-based and programmatic efforts to educate people about nutrition and healthy eating, most of the American public does not follow the Dietary Guidelines.

Accordingly, the population scored lower on the Healthy Eating Index (HEI) from 2005 to 2016, as revealed in the DGA Survey 2020-2025. The report also states that 17% of American adults followed a special diet between 2015-2018.

Given the importance of dietary quality to long-term health, the quality of the American diet needs improvement. However, this requires detailed knowledge of what Americans eat or popular fad diets in America.

About the study

In the current study, researchers identified the most “popular” fad dietary patterns in the United States and used HEI scores to assess their dietary value compared to DGAs.

First, two independent researchers compiled a database of definitions and food characteristics from peer-reviewed sources, websites, popular books, and blogs, where they specifically used the keyword “fad diet” to identify common themes.

Common themes that appeared frequently were used as a framework to establish a comprehensive working definition of a fad diet.

Next, they thoroughly searched Google Trends© using the most searched terms or phrases related to fad diets to identify ‘popular’ fad dietary patterns for inclusion in the current study.

They conducted an initial search using the keyword “diet,” which yielded 25 dietary patterns. However, after elimination based on similarity, relevance, and inclusion and exclusion criteria, eight fad dietary patterns made it into the final evaluation.

Then, the researchers identified the specific characteristics of each popular fad dietary pattern and their mechanism(s) of action on weight loss or health outcomes. These parameters were caloric restriction, micronutrient composition, restricted food components, required supplements and special diets.

The researchers used the functional parameters of popular fad dietary patterns to create one-week menus similar to how clinical dietitians create meal plans for patients. They ensured that the dietary quality of these menus complied with the DGA to the highest possible extent.

The team used the Automated Self-Administered 24 Hour (ASA24®) Dietary Assessment Tool to analyze dietary intake data and assign HEI-2015 scores on a range of 0-100, where 100 indicates full and zero indicated low adherence to DGA.

The ASA24® tool also collected information on specific foods, portion sizes, beverages, and condiments on each sample menu, which helped researchers calculate means and standard deviations (SDs) for each nutrient.

Based on this, they determined whether these menus met micronutrient requirements for both men and women aged 19–50 years based on Recommended Dietary Allowances (RDAs).


In the current synthesis, the team categorized popular fad dietary patterns as least, moderately, and most restrictive.

DGA-adherent, plant-based/vegan, and fasting diets were the least restrictive. Military, paleolithic and low-fermentable oligosaccharides, disaccharides, monosaccharides and polysaccharides (FODMAP) diets were moderately restricted.

Meanwhile, ketogenic, carnivorous and liquid diets were the most restrictive.

After maximizing DGA adherence for each popular fad dietary pattern, total HEI scores ranged from 26.7 to 89.1 for carnivore and low-FODMAP diets, respectively. Total caloric intake was highest and lowest at 2,143 and 1,302 kcal/day in liquid and non-vegetarian diets, respectively.

The majority of adequacy factors for fruits, vegetables and protein had high adequacy factor scores. Other popular fad dietary patterns include ketogenic, carnivorous, and liquid-free diets that maximize vegetable, fruit, and protein intake.

ASA24 classifies whole grains versus refined grains according to the theoretical menu. Therefore, whole grains consistently scored low, indicating submaximal adherence to all popular fad dietary patterns. Similarly, dairy/milk substitutes showed submaximal adherence to six popular fad dietary patterns. In contrast, except for DGA-compliant, military, and liquid diets, the fatty acid ratio of the other fad dietary patterns scored the highest points.

On the moderation component scale, sodium scores were consistently submaximal, indicating that most fad dietary patterns supplement excessive sodium, whereas refined grains, saturated fat, and added sugar scored high, representing low consumption.

Exceptionally, ketogenic and carnivore diets provide high amounts of fat from animal products.

In the micronutrient analysis, calcium, vitamin D, potassium, and fiber emerged as nutrients of concern due to their low intake by Americans.

Notably, vitamin D was only adequately supplemented by the Paleolithic diet, whereas calcium was adequate in all but the Paleolithic, carnivorous, and ketogenic diets.

Furthermore, all but the ketogenic and carnivore diets were potassium adequate, which also lacked fiber. With the exception of carnivorous and ketogenic diets, all other diets were, on average, concerned about insufficient vitamin E and vitamin D intake.


Overall, the current study analysis showed that if carefully planned to follow maximal amounts of DGA, some popular fad dietary patterns have the potential to achieve HEI scores greater than 80.

Five fad diets reached the cut-off threshold for high dietary quality, represented by high HEI scores. These were low-FODMAP, vegetarian, military, fasting and DGA-compliant diets. Despite problematic nutrient adequacy, the ketogenic diet has also shown the potential to achieve higher HEI scores.

Furthermore, this analysis suggested that small changes in dietary pattern parameters yield promising strategies for improving diet quality.

In conclusion, many misconceptions exist about the “proper” way to eat. However, even popular dietary patterns have the potential to promote health.

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