Should I Drink Protein Shakes if I'm Underweight? A Guide to Healthy Weight Gain

October 10, 2025 •

5 min read

For many, gaining weight can be just as challenging as losing it, requiring a consistent caloric surplus. Understanding if and how to use protein shakes can be a game-changer for those asking, Should I drink protein shakes if I'm underweight?

Quick Summary

Protein shakes can be a helpful tool for underweight individuals aiming to gain mass, especially when combined with a calorie-dense diet and strength training, but should not replace whole food meals.

Key Points

Start with a Calorie Surplus: Healthy weight gain requires consistently consuming more calories than you burn, ideally an extra 300-500 kcal per day for gradual progress.
Supplements, Not Replacements: Use protein shakes as a supplement to your regular, balanced diet of whole foods, not as a replacement for full meals.
Pair with Strength Training: Combining shakes with a resistance training program helps ensure weight is gained as lean muscle mass rather than unhealthy fat.
Choose the Right Shake: While mass gainers are an option, customizing a homemade shake with whole foods like oats, nuts, and fruit is a healthier and often more budget-friendly approach.
Watch for Added Sugars: Be mindful of pre-made shakes or powders with high levels of added sugar and artificial sweeteners, which can contribute to unhealthy weight gain.
Consult a Professional: Speak with a doctor or dietitian before beginning any weight gain regimen to rule out underlying health issues and receive personalized guidance.

Understanding Healthy Weight Gain

For individuals with a low body mass index (BMI), gaining weight healthily is about more than just increasing calorie intake. The goal is to build lean muscle mass and healthy fat stores, not simply to add pounds from junk food. A balanced, nutrient-rich diet forms the bedrock of any successful weight gain plan, with a focus on creating a consistent calorie surplus—consuming more energy than your body burns. A doctor or registered dietitian can help determine the appropriate caloric surplus, which for many is an extra 300 to 500 calories per day to achieve a steady, healthy gain.

The Role of Protein in Building Mass

Protein is the building block of muscle tissue, and consuming an adequate amount is crucial for muscle protein synthesis, the process of repairing and building new muscle. For those struggling to meet high protein needs through diet alone, protein powders offer a convenient and concentrated source of this essential macronutrient. Simply adding a scoop to a meal or shake can significantly increase the protein content without adding excessive volume, which is ideal for people with a smaller appetite.

How Protein Shakes Aid Weight Gain

Protein shakes can be a highly effective strategy when used correctly to supplement a balanced diet. Here’s why they are beneficial:

Convenient Calorie Booster: When you have a poor appetite or a fast metabolism, consuming large volumes of solid food can be difficult. A high-calorie protein shake or smoothie is easier to drink and provides a concentrated dose of calories, protein, and other nutrients. You can easily customize homemade shakes with calorie-dense additions like whole milk, nut butters, and oats to boost energy content significantly.
Support Muscle Growth: For healthy weight gain, it's vital to pair increased caloric intake with resistance or strength training. A protein shake consumed after a workout provides the amino acids needed to repair and build muscle tissue, directing the extra calories toward lean mass rather than fat. Studies have shown that protein supplementation combined with resistance training can lead to greater gains in lean body mass.
Filling Nutrient Gaps: Busy schedules can lead to missed meals or grabbing unhealthy, high-sugar snacks. Protein shakes offer a quick, nutritious alternative that helps maintain a consistent calorie surplus throughout the day. They ensure you don't miss an opportunity to fuel your body with quality nutrients.

Protein Shakes vs. Whole Foods

It is important to remember that protein shakes are a supplement, not a meal replacement. While convenient, they lack many of the vital nutrients found in whole foods. A diet consisting of only shakes would lead to nutritional deficiencies.

Comparison of Protein Sources for Weight Gain


Feature	Protein Shakes (e.g., Mass Gainer)	Whole Food Sources	Homemade Calorie-Boosted Shakes
Convenience	Very High. Quick to prepare and consume.	Varies. Requires meal prep and cooking time.	High. Customization is quick once ingredients are on hand.
Nutrient Profile	Often fortified, but can lack the full range of micronutrients and fiber found in whole foods.	Offers a broad spectrum of vitamins, minerals, fiber, and healthy fats naturally.	Highly customizable; can be packed with nutrients from whole foods like fruits, nuts, and dairy.
Cost	Can be more expensive over time, especially for high-quality products.	Typically more budget-friendly and sustainable for long-term use.	More affordable than pre-made supplements and allows control over ingredient quality.
Satiety	Less filling than a solid meal, which is a benefit for those with low appetite but can also lead to overconsumption.	More satiating due to fiber and volume, which can be challenging for those with low appetite.	Can be managed by adjusting ingredients like oats for sustained energy and fullness.

Choosing the Right Shake and Using It Safely

Not all protein supplements are created equal. The best choice depends on your specific needs. Mass gainers are specifically formulated for those with very high-calorie needs, containing a mix of protein, carbohydrates, and fats. For most underweight individuals, a high-quality whey protein concentrate blended with calorie-dense whole foods is an excellent option. If you have lactose intolerance or follow a vegan diet, plant-based protein blends (e.g., pea, soy, hemp) are good alternatives.

To use shakes safely and effectively, consider the following tips:

Prioritize Whole Foods First: Build your diet around nutrient-dense, calorie-rich whole foods like full-fat dairy, eggs, nuts, avocados, and whole grains. Use the shake to supplement this, not replace it.
Create Homemade Shakes: Blending a simple protein powder with ingredients like whole milk, bananas, oats, and peanut butter is a cost-effective and healthier way to create a high-calorie shake.
Combine with Exercise: To ensure weight is gained as muscle, not just fat, incorporate strength or resistance training into your routine. Exercise also helps stimulate appetite.
Monitor Your Intake: Over-relying on protein shakes can still lead to unhealthy fat gain if not accompanied by exercise. Use shakes as a tool to bridge calorie gaps, not as a shortcut to bypass a balanced diet.
Check Ingredients: Be wary of shakes with excessive added sugar or artificial ingredients, which are common in many pre-made and mass gainer products.

Maximizing Results with a Complete Strategy

For sustainable, healthy weight gain, a holistic approach is best. This means incorporating lifestyle changes beyond just adding protein shakes.

Eat More Frequently: Instead of large, overwhelming meals, eat smaller, more frequent meals and snacks throughout the day. This is often easier for those with smaller appetites.
Don't Drink Before Meals: Drinking large amounts of water or other low-calorie beverages before a meal can fill you up, leaving less room for food. Drink calorie-dense liquids like milkshakes or smoothies between meals.
Get Enough Sleep: Proper rest is essential for muscle repair and growth. Aim for 7-9 hours of quality sleep per night.
Seek Professional Advice: Consult a healthcare provider or registered dietitian to rule out any underlying medical causes for being underweight and to develop a personalized nutrition plan. They can guide you on the appropriate calorie and protein targets for your body.

In conclusion, protein shakes are a viable tool for underweight individuals, providing a convenient way to boost calories and protein. However, they should always complement a diet rich in whole, nutrient-dense foods and be paired with regular strength training for healthy muscle gain. With the right strategy and professional guidance, they can be an effective part of your journey toward a healthier weight.

Visit the NHS website for more tips on healthy weight gain.

Frequently Asked Questions

No, simply drinking protein shakes will not guarantee healthy weight gain. Weight gain occurs when you consume more calories than you burn. Without a caloric surplus from a balanced diet and without pairing shakes with strength training, the extra calories could be stored as fat.

For most underweight individuals, a high-quality whey protein concentrate blended with calorie-dense whole foods (like whole milk, oats, and nut butter) is ideal. Alternatively, mass gainer shakes offer high calories but should be chosen carefully to avoid excessive sugar and additives.

Potential side effects can include bloating, gas, or digestive discomfort, especially for those with lactose intolerance. Some shakes, particularly low-quality ones, may also contain harmful additives or heavy metals.

Drinking 1 to 2 protein shakes per day is generally effective for healthy weight gain, in addition to balanced, regular meals and snacks. It's best to use them to supplement your diet, such as after a workout or as a mid-day snack.

Homemade shakes offer more control over ingredients, allowing you to avoid excessive sugars and artificial additives. They can be more cost-effective and nutrient-dense by adding whole foods like fruits, oats, and healthy fats.

If you are lactose intolerant, opt for plant-based protein powders such as pea, soy, or hemp protein. You can mix these with non-dairy milks or water and still create a calorie-dense shake with other additions.

Yes, but it is not recommended for healthy weight gain. The extra calories from the shake will lead to weight gain, but without the stimulus of strength training, this will likely be in the form of fat rather than muscle mass, which is less healthy.