Breaking Down Fad Diets: The Truth Behind Keto, Paleo, and More

Ah, fad diets—the promise of beach-ready abs by next month, “you too can shed years of bad habits with a few simple rules!”

Fad diets aren’t new; they’ve been around for as long as humans have been looking for fast solutions to weight loss. The cabbage diet of the 80s gave way to the Atkins diet craze of the 90s, and then juice cleanses of the early aughts. Let’s dive into the phenomenon, why they persist, and how they stack up against science.

What Defines a Fad Diet?

A fad diet usually shares these key traits:

• Rapid Results: Promises weight loss or health improvements in an unrealistically short timeframe.
• Strict Rules: Often eliminates entire food groups or restricts specific macronutrients (fat, carbs, protein).
• Minimal Evidence: Backed more by testimonials and buzzwords than peer-reviewed research or containing just enough science linked through conjecture, it is pseudoscience.
• Unsustainable: Hard to maintain long-term, leading to weight regain or health backslide.

Weight loss on any diet is only achieved when there is a calorie deficit, meaning the calories consumed are less than the calories burned.

(meme from r/coolguides on Reddit)

Why Fad Diets Appeal

Fad diets tap into psychology and desperation:

• Instant Gratification: When people are frustrated with slow progress, these diets promise big changes fast.
• Simplicity: Eat this, not that—no ambiguity, e.g., ‘I don’t eat between 7 pm and 11 am.’
• Marketing: Influencers and before-and-after photos sell the dream.
• Novelty: “Cutting-edge” claims (often pseudoscience) make them sound revolutionary.

Let’s dive into some popular named diets and see if any are destined to become candidates for the Fad Diets Hall of Fame. (Each header in the following section will link to its subreddit.)

Popular Named Diets

Keto Diet

• Overview: This is the Atkin’s Diet’s modern cousin, the ketogenic diet focuses on high fat, moderate protein, and very low carbohydrates, aiming to shift the body into ketosis, where fat is used as the primary energy source.
• Popularity Reasons: Many are drawn to keto for its reputation for promoting rapid weight loss and supporting metabolic health. It’s particularly popular among those with type 2 diabetes, as it can aid in blood sugar control.One area where keto is proven is in kids with epilepsy; it is associated with marked seizure reduction, with effectiveness rates of ≥50% and even 100% in some cases. These outcomes are attributed to depriving the brain of glucose, which triggers ketosis and alters brain energy metabolism to reduce seizure activity.
• Concerns: Long-term adherence can be challenging, and there are concerns about heart health due to high fat intake​. A 2023 umbrella review titled “Ketogenic Diet and Multiple Health Outcomes” synthesized findings from 23 meta-analyses to evaluate the effects of ketogenic diets on various health outcomes.  While the keto combined with physical activity effectively reduced body weight, it was also linked to increased levels of low-density lipoprotein cholesterol (LDL-C), total cholesterol, and cortisol. These findings suggest that while the diet may benefit weight management, its long-term effects on cardiovascular health warrant careful consideration. Moreover, keto has been found to decrease testosterone levels. More research is needed on this to understand short-term versus long-term changes.

Intermittent Fasting (IF)

• Overview: IF involves cycling between periods of eating and periods of fasting, with popular methods like 16:8 (16 hours fasting, 8 hours eating) and the 5:2 approach (two days of very low-calorie intake per week).
• Popularity Reasons: Many appreciate its flexibility and the potential to improve metabolic health and energy. Studies suggest IF can help reduce body weight, improve markers like insulin sensitivity, and boost autophagy​. Autophagy is like your body’s natural recycling system. When you go without food for a while, your cells start cleaning house. They break down and reuse old, damaged, or unnecessary parts to make energy and repair themselves.
• Concerns: Prolonged fasting might be counterproductive for those with high physical demands or unstable blood sugar levels. Reaching autophagy might not be realistic for some folks lifestyles, as studies suggest that glycogen stores (the body’s immediate energy reserves) are depleted after about 12-16 hours of fasting, signaling a metabolic shift that promotes autophagy, it becomes more pronounced as fasting extends to 24-48 hours.

If your focus is just weight loss, not the other benefits of IF, you should know that several studies have compared IF with continuous calorie restriction to determine its effectiveness in weight loss. The findings generally indicate that when calorie intake is matched, the weight loss results are similar between the two approaches.

Paleo Diet

• Overview: Emphasizing “ancestral” foods (lean meats, fish, fruits, vegetables, nuts, seeds) and eliminating processed foods, dairy, grains, and legumes, the Paleo diet is intended to mirror what our early ancestors might have eaten.
• Popularity Reasons: Many find the Paleo diet appealing for its emphasis on whole foods and the promise of improved energy and digestive health. It’s also thought to support lean muscle mass, which appeals to active men​. The Paleo diet showed significant short-term improvements in key markers of metabolic syndrome compared to control diets. These include reductions in waist circumference, triglycerides, fasting glucose, and blood pressure. It also improved HDL cholesterol levels and insulin sensitivity, making it particularly effective for addressing risk factors associated with cardiovascular disease and diabetes. Paleo’s impact on testosterone has not been rigorously studied.
• Concerns: Scientists point out that excluding entire food groups can lead to nutrient deficiencies, particularly calcium, vitamin D, and certain B vitamins, and the Paleo diet may be challenging to maintain long-term due to food restrictions and the cost to acquire mainstays of the diet. Concerns are similar to those of keto, such as what the diet’s prescribed intake of saturated fats will have on long-term cardiovascular health.

Carnivore Diet

• Overview: An extreme form of low-carb dieting promoted by Shawn Baker, the Carnivore diet focuses solely on animal products—meat, fish, eggs, and certain dairy, with no plant-based foods.
• Popularity Reasons: Some folks are attracted to the simplicity of this all-meat diet, its promise of weight loss, and its supposed anti-inflammatory effects.
• Concerns: It is highly restrictive and may lead to nutrient deficiencies, with risks for heart and kidney health due to high saturated fat intake. Fiber anyone? Shawn Baker conveniently has a book to sell you titled The Carnivore Diet. Out of all the named diets on this list, this diet gets the nomination for the Fad Diet Hall of Fame from the Grannus team since we have a lot of science that shows the benefits of vegetables and the harmful risks of high-saturated foods.

Whole30

• Overview: Whole30 is a 30-day elimination diet that excludes sugar, alcohol, grains, dairy, and legumes, focusing on whole foods to “reset” the body. In addition to some food nuances, it differs from Paleo in that it is not intended to be a long-term lifestyle.
• Popularity Reasons: Many like the structured approach, using it to reset after periods of unhealthy eating or to help identify food sensitivities and promote short-term weight loss. Identifying that particular food that has been causing your bloat, fatigue, and other digestive issues can be life-altering for folks.
• Concerns: Its strict rules can be hard to follow, and reintroducing foods afterward can be challenging if long-term changes aren’t made. If maintained on a long-term basis, the risk of nutritional deficiencies similar to those of the Paleo diet can occur.

Bottom Line

Lasting change with sustainable improvements isn’t sexy. It’s work and it can be hard to change, really hard. Even with the rise of GLP-1 medications that help promote weight loss, there’s still the debate of  “taking the easy way out via an injection” versus doing ‘the work’ of losing the weight through traditional diet and exercise approaches. (Current data says 1 in 5 people won’t experience meaningful weight loss using a GLP-1 medication.)

In general, we at Grannus tend to subscribe to the belief that any weight loss that combats obesity is good, as long as it is done with a healthy approach and a view towards sustaining it long-term.  Fad diets are a quick hit but rarely effective in the long run, and some of the worst offenders cause more harm than good. They may jumpstart weight loss or health improvements, but a balanced, evidence-based approach is the key to lasting change. (That’s why we talk so much about the Mediterranean Diet–it checks all the boxes.) If the latest miracle diet tempts you, remember: your health journey isn’t a sprint—it’s a marathon. And no marathon is won on cabbage soup alone.

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