Protein is an important nutrient for weight loss.
Getting enough can boost your metabolism, reduce your appetite and help you lose body fat without losing muscle.
Protein shakes are an easy way to add more protein to your diet, and have been shown to help with weight loss.
This article explains everything you need to know about protein shakes and how they affect your weight.
What Are Protein Shakes?
Protein shakes are drinks made by mixing protein powder with water, although other ingredients are often added as well.
They can be a convenient addition to the diet, especially when access to quality high-protein foods is limited.
Although most people don’t need them to meet daily protein requirements, they can also be useful if you need to increase your intake for some reason.
You can buy protein powder and mix it yourself, but you can also get many different brands of pre-made liquid shakes.
Some of the most popular types of protein powder on the market are:
- Whey protein: Quickly absorbed, dairy-based. Contains all the essential amino acids (1).
- Casein protein: Slowly absorbed, dairy-based. Contains all essential amino acids (1).
- Soy protein: Plant-based and contains all essential amino acids. Also contains soy isoflavones, which may provide some health benefits (2).
- Hemp protein: Plant-based and high in omega-3 and omega-6 fats, but low in the essential amino acid lysine (3).
- Rice protein: Plant-based and low in the essential amino acid lysine (3).
- Pea protein: Plant-based and low in the non-essential amino acids cystine and methionine (4).
Some brands contain a mix of different types of protein powder. For example, many plant-based brands combine types to complement each other’s amino acid profile.
Bottom Line: Protein shakes can contain different types of protein, each with its own characteristics.
Protein Shakes Decrease Hunger and Appetite
Protein can decrease hunger and appetite in two main ways.
First, it increases levels of appetite-reducing hormones like GLP-1, PYY and CCK, while reducing levels of the hunger hormoneghrelin (5, 6, 7, 8, 9):
Second, protein helps you feel full for longer (10, 11).
In one study, a high-protein breakfast helped participants consume up to 135 fewer calories later in the day (12).
In another, overweight men who had been on a weight loss diet increased their protein intake to 25% of total calories. This increase cut cravings by 60% and late-night snacking by half (13).
Increasing protein intake from 15% to 30% of total calories helped participants in another study consume 441 fewer calories per day without actively trying to limit their portions (14).
What’s more, by the end of the 12-week study period, they had lost an average of 11 lbs (5 kg) (14).
These shakes can be a convenient way to add extra protein to your diet. However, keep in mind that too much can still lead to excess calories.
Another study found that shakes containing 20-80 grams of protein all decreased hunger by 50-65%, regardless of the amount of protein in their shakes (15).
So if you’re trying to lose weight, 20 grams per shake seems sufficient to reduce hunger.
Bottom Line: Protein can decrease your appetite by affecting your hunger hormones. It can also help you feel full for longer, which can help you eat less and lose body fat.
Protein Shakes May Increase Metabolism
High protein intake can boost your metabolism, helping you burn slightly more calories each day (16, 17).
That’s in part because a high-protein diet — especially when combined with strength training — may help you build muscle.
This can speed up your metabolism because muscle burns more calories than fat.
One study gave obese participants shakes with either 200 or 0 grams of extra protein per week.
Those given the protein gained 2.8 lbs (1.3 kg) more mass following a 13-week training program (18).
In another study, researchers gave participants a combination of foods and shakes providing either 0.5 g/lbs or 1.1 g/lbs (1.2 g/kg or 2.4 g/kg) of protein per day.
After 6 weeks, those on the higher-protein diet gained 2.4 lbs (1.1 kg) more muscle and lost 2.9 lbs (1.3 kg) more fat (19).
It should be noted, however, that your ability to gain muscle during a weight loss diet may depend on the amount of muscle you already have (20).
Protein can also increase metabolism because of the amount of calories needed to digest and metabolize it. This is known as the thermic effect of food (TEF).
For instance, 15-30% of protein calories are burned during digestion, while only 5-10% of carb calories and 0-3% of fat calories are burned during digestion (21).
Bottom Line: Protein helps boost metabolism because a lot of energy is spent digesting and metabolizing it. It also helps you build muscle, which burns more calories than fat.
Protein Shakes May Help You Lose Weight and Belly Fat
Researchers generally agree that high-protein diets can help you lose more fat, especially fat from the belly area (22, 23).
In one study, participants on a diet providing 25% of calories as protein lost 10% more belly fat after 12 months than those eating half that amount (24).
In another, participants given an extra 56 grams of whey protein per day had lost 5 lbs (2.3 kg) more at the end of a 23-week study period, despite not consciously changing anything else in their diet (25).
A separate study compared the effect of various weight loss diets. The participants consuming more protein lost 31 lbs (14.1 kg) in 3 months — 23% more than those consuming less (26).
In one final study, participants on diets providing 30% of calories from protein lost 8.1 lbs (3.7 kg) more than those on diets providing 15% of calories from protein (13).
Bottom Line: Protein shakes are a convenient way to increase your daily protein intake. This can help boost fat loss, especially from around your mid-section.
Protein Shakes May Also Prevent Muscle Loss and Metabolic Slowdown
Weight loss diets often cause you to lose muscle, which can slow down your metabolism. This makes it easier to gain all the weight back (and more) once you go off the diet.
A high protein intake combined with strength training can help prevent part of this muscle loss and metabolic slowdown (27, 28, 29).
In fact, researchers reported that participants’ metabolism decreased less on a weight loss diet providing 36% of calories as protein than on a diet providing about half that amount (30).
Evidence shows that consuming a daily protein shake as part of a weight loss diet may make muscle maintenance up to three and a half times more efficient (31).
A study of athletes compared weight loss diets providing either 35% or 15% of calories from protein. Both diets helped participants lose about the same amount of fat, but those consuming more protein lost 38% less muscle mass (32).
A recent review further notes that weight loss diets that exceed 0.5 g/lbs (1.0 g/kg) of protein per day can help older adults retain more muscle and lose more fat (33).
Bottom Line: Protein shakes consumed during a weight loss diet can help prevent muscle loss and metabolic slowdown. This is particularly effective in combination with strength training.
Protein Shakes May Help Prevent Weight Re-Gain After Weight Loss
Protein’s effect on metabolism, appetite and muscle mass may also keep you from regaining the fat you worked so hard to lose.
One study reports that participants given more protein lost more weight and maintained their results better than those given less.
In fact, the high-protein group regained only 9% of the lost weight, whereas the low-protein group regained 23% (26).
Another study gave participants who just completed a weight loss intervention a supplement that provided 48.2 grams of protein per day.
Participants who took the supplement felt more full after meals and had regained 50% less weight 6 months later, compared to those given no supplement (34).
A separate study noted similar effects with a supplement that provided only 30 grams of protein per day, once again showing that more is not necessarily better (35).
Bottom Line: Additional protein, whether from shakes or whole foods, can help minimize the amount of weight you regain after weight loss.
Which Type of Protein is Best?
Different types of protein have different effects on the body.
For instance, whey is more quickly absorbed than casein, helping you feel less hungry in the short-term.
One study reports that 56 grams of whey protein per day helped overweight and obese participants lose 5 lbs (2.3 kg) more fat than the same amount of soy protein (25).
Another describes whey as 3 times more effective at maintaining muscle-building ability during a weight loss diet than soy protein (31).
That being said, not all studies agree that whey is superior. For example, one report notes that the faster hunger-reducing effect results in no differences in the amount of calories consumed at meals (36).
Furthermore, several reviews report equal amounts of fat loss with use of whey, soy, rice or egg-protein supplements (37, 38).
One final factor to consider is the protein’s quality.
Whey, casein and soy contain all the essential amino acids your body needs.
On the other hand, rice and hemp protein are low in the essential amino acid lysine, and pea protein is also low in the non-essential amino acids cystine and methionine.
That being said, these deficiencies likely don’t cause a problem unless if shakes are the only source of protein in your diet.
Also, many plant-based protein powders mix different sources so that the mixture contains all the essential amino acids.
Bottom Line: The exact type of protein powder you have in your shakes should not make a major difference for fat loss. Some studies show an advantage for whey, but the evidence is mixed.
Dosage and Side Effects
Taking 1 shake per day should be a good way to start.
It is best to take it either before or instead of a meal, with 1 or 2 scoops of protein powder in the shake.
Mixing it with water, ice and perhaps a piece of fruit in a blender is a simple way to create a delicious and satisfying shake.
Side effects such as bloating, cramps, gas and diarrhea may occur if you’re lactose intolerant and drinking shakes made with whey or casein.
These symptoms can be simply avoided by switching to protein powders not derived from dairy, such as egg, pea, soy, hemp or rice protein powders.
Of note, high-protein diets were once thought to have negative impacts on kidney and bone health, but newer research shows this is not true.
In fact, high protein intakes were never shown to cause any kidney damage in healthy people. However, lower-protein diets may be beneficial for those with existing kidney issues (39, 40).
Protein is also an essential nutrient for bone formation and maintenance, and reviews show that there is no reason to restrict your intake to improve bone health (41, 42).
Most studies report that total protein intakes of between 0.5-1.0 g/lbs (1.2-2.2 g/kg) per day provide most beneficial effects for weight loss.
This amount of protein normally represents around 25-35% of the calories you consume in one day and is generally considered safe.
You can read more about that here: How Much Protein Should You Eat Per Day?
Bottom Line: Taking one shake per day is a good way to start, with 1 or 2 scoops of protein. Some people may experience digestive side effects.