Is a Low-Carb or Low-Fat Diet Better for Weight Loss?

Low-carb vs low-fat diets for weight loss.

The debate goes round and round.

30 years ago, fat was the enemy and low-fat diets were heralded as the key to cardiovascular health. For much of the past 20 years, the situation has been reversed. Carbs are to blame for all that ails society, and fat has been elevated to the spotlight.

Side note: Spend enough time on health and fitness, and you’ll quickly realize there’s a lot of pendulum swinging. The same extends to dietary supplements as well. Supplements that fall out of favor eventually resurface as some “long lost” relic that promises great results, but more often than not passes out of the limelight and waits for a return.

Anyway, back to the issue at hand: low-carb vs low-fat diets for weight loss, which is better?

Let’s discuss.

What is a Low-Fat Diet?

Today, low fat diets are nutrition plans where 30% or less of daily calories come from fat (earlier low-fat diets advocated for an even lower percentage of daily fat intake between 10-20%). Generally speaking, a food is considered “low fat” if it contains 3 grams of fat (or less) per 100 calories.[1]

In the late 80s and 90s, low-fat diets were touted to be heart healthy as prior research by Ansel Keys and colleagues, which has since come under heavy scrutiny, found an association between high saturated fat intake and heart disease.

This resulted in the low-fat/no-fat craze where natural fats like butter, lard, dairy fats, and beef tallow were replaced with cheap, highly refined carbohydrates and artificial trans fats. So your favorite cookies, cakes, frozen yogurts, etc. were “fat free” but teeming with simple carbs and added sugars.

This brought about two big issues:

1. Man-made trans fats (partially hydrogenated oils) are actually worse for cardiovascular health than natural animal fats humans have been cooking with for centuries
2. Replacing fats in packaged foods with cheap carbohydrates led to excessive consumption of sugars which increase the risk of metabolic disorders and hyperglycemia (high blood sugar).

It is worth mentioning that other studies have shown that reducing dietary fats (particularly saturated and trans fats) can improve cardiovascular risk factors and weight loss.[2,3]

What is a Low-Carb Diet?

Low-carb diets restrict carbohydrate intake in favor of increasing dietary fat and protein intake. Depending on which low-carb method you follow, your daily carb intake will range from 10-30% of total daily calories. Ultra-low carb diets like the ketogenic diet set an upper limit of carbs at 10%. For reference, the Institute of Medicine (IOM) suggests individuals consume between 45-65% of daily calories from carbohydrates.[4] Any lower than 45% carb intake is usually considered “low carb.”

Protein typically accounts for 30% of daily calories and fat makes up the rest.

Low-carb diets gained popularity from the belief that lowering insulin levels improves weight loss. Insulin is an anti-catabolic hormone that increases in response to carbohydrate intake. When insulin levels rise, the body limits burning fat for energy, and shifts to burning carbohydrates and storing them in muscles and the liver (in the form of glycogen). It was thought that by keeping insulin levels on the lower end, the body would be burning more fat for fuel, which would ultimately support weight loss.

However, this reasoning tends to overlook the fact that total calorie intake plays a prominent role in weight changes.

Similar to low-fat diets, low-carb proponents also have a stable of studies to point to demonstrating their effectiveness for weight loss.[5] Still, there is concern in the medical community regarding the safety of low-carb, high-fat diets on cardiovascular risk factors.[4]

Research Update: Low-Fat vs Low-Carb Diets for Weight Loss

In recent years, there have been several notable studies directly comparing low-fat vs low-carb diets for weight loss.

The first was the famous DIETFITS study, published in 2018, which tracked 600 adults over 12 months (an entire year) and concluded that there was “no significant difference in 12-month weight loss” between low fat or low carb diets.[6]

A 2020 cohort study found that both low-carb and low-fat diets were associated with lower mortality, and unhealthy low-carb and low-fat diets were associated with higher mortality.[7] The results of this study suggest that food quality also has an impact on health outcomes beyond simple macronutrient content.

A small study published in 2021 had 20 adults live in a metabolic ward (the most accurate method we currently possess for measuring all food intake and energy expenditure) and randomized to a minimally-processed, plant-based, low-fat diet (10.3% fat, 75.2% carb, 14.5% protein) or a minimally processed, animal-based, ketogenic diet (75.8% fat, 10.0% carb, 14.2% protein). Both diets also included the same amount of non-starchy vegetables.[8]

Individuals were allowed to eat as much as they wanted (ad libitum) and followed each diet for 2 weeks. At the end of the study, researchers found that the low-fat diet led to less calorie intake than the low-carb diet over the 2 week period. The study was small and relatively short-term, but only the low-fat led to a significant loss in body fat.[8]

Most recently, a secondary analysis was done on the data obtained from the 2018 DIETFITS study to determine what has the greater impact on weight loss and improvements in cardiovascular risk factors, food quality or macronutrient composition (low-carb vs low fat diets).[9]

Upon further review of the data, researchers concluded that the individuals with the greatest success in reducing BMI and improving cardiovascular risk factors were those with the highest adherence to their particular diet and higher quality foods.[9] As we mentioned above, weight loss between the low-fat and low-carb groups was similar (less than one kilogram difference in weight loss over 12 months).[6]

Key Takeaways

When it comes to low-carb vs low fat for weight loss, finding a diet that you can stick to tends to lead to better weight loss/maintenance outcomes. In other words, low-carb or low-fat diets can be equally effective for weight loss.

The trick, much like with exercise, is to find the method that works for YOU!

So long as you are focusing on high quality foods, staying physically active (cardio & resistance training), and hitting your calorie/macronutrient targets for the day, you can lose weight following either low carb or low fat diets.

How to Track Your Nutrition

You can go old school with pen and paper, which works fine, but an easier way to see how you’re doing with your nutrition goals is to log your food in the 1UP Fitness App. Within the app, you can tailor your calorie and macronutrient targets to your preferences as well as get FREE customized nutrition and training recommendations to help you achieve your fitness and physique results.

For added support sticking to your weight loss diet, here are a few suggestions:

• Prioritize protein: Your body burns more calories digesting protein that it does carbohydrates or fats. Protein also is more satiating (meaning it keeps you feeling fuller) than either carbohydrates or protein. As such, make protein the main component of each meal, and add carbohydrates and fats to it to meet your calorie goals. If you have trouble hitting your protein goals each day, try having a serving of whey protein or vegan protein in between meals.
• Eat Fiber-Rich Foods: Plant foods like fruits, veggies, whole grains, nuts, seeds, and legumes contain complex carbohydrates, which deliver a steady release of energy into the body, vitamins, minerals, and fiber. While our bodies can’t digest fiber, it helps to fill us up, promote GI health, and nourish the good bacteria in our gut. Current fiber intake recommendations are 25 grams for women and 38 grams for men. For help reaching your fiber goals, make sure to eat enough whole foods and incorporate a serving of 1UP Fiber Plus when necessary.
• Consider Appetite Support: Diet fatigue and hunger are two of the biggest causes for individuals abandoning their diet plans. Diet fatigue can be combated with building your diet around foods you enjoy and having the occasional refeed day if you’re really dragging. Experiencing small bouts of hunger is pretty normal when dieting, especially if you’ve been dieting for several weeks. For added appetite control, it may be helpful to use a suppressant, such as 1UP Appetite Suppressant which is stimulant-free and contains natural ingredients, including fiber, to help reduce cravings.

References

1. Bhandari P, Sapra A. Low Fat Diet. [Updated 2023 Feb 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK553097/
2. Dhaka V, Gulia N, Ahlawat KS, Khatkar BS. Trans fats-sources, health risks, and alternative approach - A review. J Food Sci Technol. 2011 Oct;48(5):534-41.
3. Tobias DK, Chen M, Manson JE, Ludwig DS, Willett W, Hu FB. Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: A systematic review and meta-analysis. Lancet Diabetes Endocrinol. 2015;3:968-979. doi: 10.1016/s2213-8587(15)00367-8.
4. Oh R, Gilani B, Uppaluri KR. Low-Carbohydrate Diet. [Updated 2023 Aug 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537084/
5. Nordmann AJ, Nordmann A, Briel M, Keller U, Yancy WS, Brehm BJ, Bucher HC. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Arch Intern Med. 2006 Feb 13;166(3):285-93.
6. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion. The DIETFITS Randomized Clinical Trial. JAMA. 2018;319(7):667–679. doi:10.1001/jama.2018.0245
7. Shan Z, Guo Y, Hu FB, Liu L, Qi Q. Association of Low-Carbohydrate and Low-Fat Diets with Mortality Among US Adults. JAMA Intern Med. 2020 Apr 01;180(4):513-523.
8. Hall KD, et al. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nat Med. 2021 Feb;27(2):344-353. doi: 10.1038/s41591-020-01209-1. Epub 2021 Jan 21. PMID: 33479499.
9. Hauser ME, Hartle JC, Landry MJ, Fielding-Singh P, Shih CW, Qin F, Rigdon J, Gardner CD. Association of dietary adherence and dietary quality with weight loss success among those following low-carbohydrate and low-fat diets: a secondary analysis of the DIETFITS randomized clinical trial. Am J Clin Nutr. 2024 Jan;119(1):1740184. doi: 10.1016/j.ajcnut.2023.10.028. Epub 2023 Nov 4. PMID: 37931749; PMCID: PMC10808819.