Whey Protein vs Plant Protein For Fat Loss: Which Is Best?

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Both whey protein and plant-based protein powders are beneficial for fat loss. 

Whey protein naturally has higher leucine levels, which improves muscle retention, and as I’ll explain later, is an important element for losing body fat.

However, when leucine content is matched across different types of plant-based proteins, the results are the same.

So, the best protein for fat loss may just be a matter of personal preference.

With that said, I’m going to share the most important information about whey vs plant protein so that you can pick the one that is best suited for your weight loss journey.

Key Takeaways

• The leucine content of your protein is one of the most important factors for determining whether your protein powder will be effective in helping you lose body fat.

• Many plant-based protein powders are considered “incomplete proteins” and therefore less effective. As such, I recommend choosing a soy protein or plant-based protein matrix (explained later), which has similar leucine contents to whey protein.

• Whey and soy isolate proteins have better digestibility and are more effective for delivering amino acids to your muscles and minimizing digestive distress.

A Note On Ethical Considerations For Whey vs Plant Protein

This article is not meant to debate any ethical considerations about animal versus plant-based sources of protein. Our goal is to review current scientific evidence (or lack thereof) regarding whether whey protein or plant-based protein powder is more effective for fat loss.

Why Is The Leucine Content In Your Protein Supplement Important For Fat Loss?

One of the ways to think about the quality of a protein source is its leucine content. 

Protein is made up of building blocks called “amino acids“.

Leucine is one of nine essential amino acids and is critical for building and repairing muscle tissue, which makes it helpful for fat loss.

Higher leucine levels not only promote muscle protein synthesis (muscle growth) but also reduce the rate of muscle protein breakdown so that you can preserve lean muscle mass.

Why is this important during a weight loss phase?

Ultimately, the more muscle you have, the more calories you burn, even at rest, which is ideal for fat loss.

For example:

Someone who weighs 158lbs and has a body fat percentage of 15% (23.7lbs of fat and 134.3lbs of lean mass) would burn approximately 1846 calories at rest.

• Someone else who weighs the same (158lbs) but has a body fat percentage of 25% (39.5lbs of fat and 118.5lbs of lean mass) would only burn 1688 calories at rest.

Being able to burn calories at a faster rate makes fat loss easier because you will be able to lose weight by eating more calories.

A person with 15% body fat will be able to lose weight by eating more calories than a person with 25% body fat.

This is why choosing protein sources with a higher leucine content that helps you to retain your current muscle mass or potentially gain more muscle is very beneficial for fat loss.

• Related Article: What Does Organic Protein Powder Do? (Is It Worth It?)

Does It Matter Whether You Take Whey Protein Or Plant Protein For Fat Loss?

Yes, there are small differences in the research when it comes to outcomes using whey protein or plant-based protein powders as supplements when trying to lose fat.

Whey protein powder has a slight edge when it comes to leucine content, the number of grams of protein per calorie, and digestibility.

So choosing protein sources higher in leucine is best for fat loss.

However, there are some plant-based protein powders on the market that can be used to get the same results (recommendations below). 

With all that said, research suggests that the most important factor for fat loss is not the protein powder you select, but rather making sure you reach your overall daily protein target while maintaining a calorie deficit.

• Related Article: How Much Protein When Cutting? (A Nutrition Coach Answers)

Differences Between Taking Whey Protein or Plant Protein For Fat Loss

There are some key differences between whey protein and plant-based protein to consider before choosing the right one for you.

Protein Quality (Leucine Content)

Animal-based protein sources generally contain more leucine than plant-based proteins.  Animal-based protein sources tend to have 8.5-10% or more leucine content, whereas plant-based protein sources average 6-8%.

• Whey protein contains about 13.6% leucine, so a scoop of protein powder with 25 grams of protein would have about 3.4 grams of leucine.

• Soy protein isolate contains about 8% leucine, so a scoop of protein powder with 25 grams of protein would have about 2 grams of leucine.

• Brown rice protein isolate contains about 6.4% leucine, so a scoop of protein powder with 25 grams of protein would have about 1.6 grams of leucine.

Many new plant-based protein powders combine different plant-based sources of protein (i.e. brown rice + pea protein) to create a “plant-based protein matrix,” which has the same amino acid profile as whey protein powder.  

• Related Article: Pea vs Whey Protein: A Nutrition Coach Explains The Differences

This study found that when amino acid profiles are equated, whey protein did not possess any unique anabolic (muscle-building) properties over plant-based powders.

A similar study saw no difference in muscle growth during resistance training when soy and whey proteins were matched for leucine content.

Key takeaway: you will either need to take more of a plant-based protein powder to get the same amount of leucine, or look for a plant-based protein matrix that provides the same amino acid profile (same amount of leucine) as an equivalent amount of whey protein powder.

Complete Proteins

A protein is considered complete when it contains all nine essential amino acids.  Incomplete proteins are lacking in one or more of the essential amino acids. Animal products and protein powders made from them are complete proteins; however, most plant-based protein powders are incomplete (except for soy).

In this study, complete proteins lead to larger increases in energy expenditure than do lower-quality proteins. This means that complete proteins cost your body more energy to digest so you burn more calories eating complete proteins, which can make fat loss easier.

Additionally, complete proteins will have everything that your body needs to build and repair muscle effectively, but plant-based proteins that are incomplete (i.e. brown rice or pea protein) will not.

That said, you can get plant-based protein powders that are complete proteins if you’re choosing protein powders made from soy or choosing a blend of plant-based sources that form a complete protein. 

For example, brown rice and pea proteins are not complete on their own but when combined, they complement one another by providing the essential amino acid that the other is missing, making the blend a complete protein.

Many popular vegan protein powders combine several different types of plant protein to create a complete protein source, with an amino acid profile that is similar to whey.

For example, Garden of Life Raw Organic Protein Powder has 15 different plant-based sources of protein, including buckwheat and quinoa, and the amino acid profile is published on the nutrition label, showing 1.8 grams of leucine per 22 grams of protein (8%).

In comparison, Dymatize ISO 100 Hydrolyzed Protein Powder (read our review of Dymatize) is a hydrolyzed whey isolate with 2.6 grams of leucine per 25 grams of protein (10%).  

Key takeaway: Choosing a protein powder that’s a complete protein is important to maximize muscle growth and repair, so it’s important to choose a whey protein or to look for a plant-based protein matrix that combines several protein sources (including buckwheat, quinoa, or soy) to create a complete protein.

Calorie & Protein Content

The average calorie and protein content for 30g of whey protein powder is ~110 calories with 21 grams of protein (0.19 grams of protein per calorie). The average calorie and protein content for 30g of plant-based protein powder is 120 calories with 20 grams of protein (0.17 grams of protein per calorie).

This means that the average total calorie and protein content is nearly identical, but there are differences from brand to brand.  

For example, Garden of Life was 130 calories with 22 grams of protein (0.17 grams of protein per calorie) and Dymatize was 110 calories with 25 grams of protein (0.23 grams of protein per calorie). You can see that plant-based protein has more fat and carbs than whey protein.

So, if you need to increase the amount of plant-based protein you’re consuming to get a higher amount of leucine to match the amount you’d get from whey protein powder, then you will end up consuming more calories, carbs, and fats.  

For example, you would need an extra 33% (10 grams) of Garden of Life to get the same amount of leucine (2.4 grams) as Dymatize, which would add 43 calories from a combination of protein, carbs, and fats.

This isn’t necessarily a concern as long as you still hit your total macros for the day.

It’s just worth paying attention to because generally people struggle to consume enough protein but hit their carbs and fats quite easily. So, choosing a plant-based protein wouldn’t necessarily solve this problem like a whey protein would.

Key takeaway: If you struggle to hit your protein intake without going over your carb and fat targets then choosing a whey protein powder with a higher amount of protein per calorie would be better. Look for products with minimal fat & carbs, and a high number of grams of protein per calorie (0.2g/calorie is great).

Digestibility

Even if a protein source looks promising in theory given its nutritional profile, it’s not worth it if you can’t digest it comfortably. For a protein to be used effectively by the body, it has to be broken down into its amino acid components.

The World Health Organization developed Protein Digestibility Corrected Amino Acid Score to give users a better idea of how easily different proteins are digested. The higher the score, the more easily the protein digests.

• Whey Protein: 1.00
• Soy Protein Isolate: 1.00
• Pea Protein Isolate: 0.53

In general, animal-based sources of protein like milk, chicken, beef, and eggs all have PDCAAS of 1.00 (the highest) whereas plant-based sources (other than soy protein isolate) have lower scores, ranging around 0.5-0.7.

Additionally, some protein powders have added ingredients that can also cause digestive distress in sensitive individuals. The most common ingredients to cause issues are artificial sweeteners and flavors, which could be present in both whey and plant-based proteins.

If your protein powder is causing you digestive distress (bloating, nausea, constipation, or diarrhea) then look for unsweetened, unflavored options, or brands that use natural sweeteners and flavoring agents.

Key takeaway: Whey protein isolate and soy protein isolate are both highly digestible forms of protein. Other plant-based proteins like pea protein and brown rice do not digest as effectively.  If you struggle to digest your protein powder, it’s going to make reaching your daily protein intake harder, and therefore negatively impact your fat loss phase.

Satiety

Protein in general helps to improve satiety by suppressing your hunger hormone for longer periods. However, another factor that impacts your level of satiety is your fiber intake because fiber takes longer to digest. So, protein powders that also contain fiber can be helpful for managing hunger and promoting fat loss.

There is research focusing on whether the type (animal or plant) of protein has an impact on the hormones that control hunger. 

In this study, participants actually lost slightly more weight (2.41kg vs. 2.27kg) on a vegetarian high-protein weight loss diet (with soy as the main source of protein) than on an animal-based high-protein diet.

However, the weight discrepancy isn’t enough to be significant and the subjects’ reports of overall satiety were also nearly identical between groups.

For this reason, they concluded that plant-based protein (specifically soy) and animal-based protein are equally as effective for appetite control during a fat-loss phase.

Key takeaway: Both animal (whey) and plant-based protein powders increase feelings of fullness, which helps manage hunger during a calorie deficit.  Protein powders with a higher fiber content (6+g per serving) can also increase satiety, but should not be consumed immediately before a workout.

• Related Articles: Do Protein Shakes Fill You Up? (6 Factors To Consider)

If Taking Plant-Based Protein Powder For Fat Loss, Which Types Are Best?

If you’re taking a plant-based protein powder for fat loss, look for soy protein isolate with additional leucine, or a plant-based protein “matrix” that combines several types of plant protein powders to get a complete amino acid profile that’s more similar to whey.

Whey protein powder is often called the “gold standard” when it comes to protein powders (hence the product Gold Standard Whey – click here to read our review).

To achieve the same benefits as a plant-based protein powder, the product must match the qualities of whey in terms of:

• Leucine content
• Amino acid profile (be a complete protein source)
• Grams of protein per calorie
• Digestibility

My top recommendation for a plant-based protein powder that meets these requirements is Now Sports Nutrition Soy Protein Isolate.

One 24-gram serving has 20 grams of protein for 90 calories (0.22 grams of protein per calorie, which is excellent), and 1.8 grams of leucine (9%).  

Increasing the serving by a third (to a total serving size of 32 grams) would provide 27 grams of protein for 120 calories and would provide 2.4 grams of leucine, which is on par with Dymatize Iso 100 (click to read our review).

I also love that this product is free of sweeteners, flavors, and carbohydrates, and only has half a gram of fat per serving.

Other brands of plant-based protein that I recommend are:

• Vega Sport Premium Vegan Protein Powder
• Garden of Life Raw Organic Protein Powder
• Truvani Plant Based Protein Powder

Types of plant-based proteins that I do NOT recommend are:

I do not recommend them because they are not complete protein sources on their own and have lower digestibility scores and lower leucine content.

• Pea protein powder
• Rice protein powder
• Hemp seed protein powder
• Pumpkin protein powder

Take Whey Protein For Fat Loss If:

• You can comfortably digest whey protein

• Want a protein powder that is naturally high in leucine

Take Plant Protein For Fat Loss If

• You have ethical or environmental considerations keeping you from consuming animal-based proteins.

Final Considerations on Whey vs Plant Protein

If you do take a plant-based protein powder, consider using soy protein or look for plant-based protein “matrix” products (blends) and take serving sizes to match the leucine content of whey.

Regardless of what type of protein powder you choose, we recommend limiting your intake to no more than 1/3 of your total daily protein intake. 

Setting an upper limit for protein powders will ensure that you’re consuming enough whole food sources of protein to meet your micronutrient (vitamins & minerals) requirements.

Other Protein Powder Comparisons:

• Grass-Fed Whey Protein vs. Regular (What To Know Before Buying)
• Protein Powder vs Pre-Made Shake: Coach Explains Which Is Best
• Whey Isolate vs Concentrate: A Coach Explains The Differences
• Whey vs Egg Protein: Differences, Pros, Cons

References

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Schoenfeld, B.J., Aragon, A.A. How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. J Int Soc Sports Nutr 15, 10 (2018). https://doi.org/10.1186/s12970-018-0215-1

van Vliet, Stephan & Burd, Nicholas & Loon, Luc. (2015). The Skeletal Muscle Anabolic Response to Plant- versus Animal-Based Protein Consumption. The Journal of nutrition. 145. 10.3945/jn.114.204305.

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