Why Protein Is Non-Negotiable for Fat Loss

Written by Mackayla Brennan

Content writer and Nutrition student 

Mackayla Brennan is a health and nutrition content writer at Hercules Supplements. She focuses on creating evidence-based content on digestion, gut health and nutrition, helping everyday Australian's translate complex research into practical dietary advice.

Calories and fat loss

When it comes to fat loss, calories matter, but the quality and composition of those calories matter too. Among the three macronutrients, protein plays a particularly important role during a calorie deficit. It helps support lean muscle mass, improves satiety, and can help maintain metabolic rate while dieting.

If your goal is sustainable, effective fat loss, getting enough protein is not optional. It is a foundational part of your nutrition strategy.

To support healthy fat loss, it is important to consume enough protein for your body, lifestyle, and activity levels. In this article, we’ll explore why protein matters so much during a fat-loss phase, and how much you may actually need.

Protein reduces cravings and increases satiety

One of the biggest challenges during fat loss is managing hunger. Of the three major macronutrients; carbohydrates, fats, and protein, protein is generally considered the most satiating.

Satiety is the state of feeling full and satisfied, where your body signals to your brain that you have had enough to eat. Protein works in several fascinating ways to regulate appetite and control food intake.

Protein has a powerful effect on the hormones that regulate hunger and fullness.

A 2020 systematic review and meta-analysis found that protein intake reduced hunger and increased feelings of fullness in the short term, while also lowering ghrelin, the hormone that stimulates appetite, and increasing satiety-related hormones such as CCK and GLP-1. These hormones send signals to your brain that you are satisfied, which may help naturally reduce overall calorie intake and make a calorie deficit feel more manageable. This hormonal shift is one of the main reasons higher-protein diets are often associated with improved appetite control and reduced snacking.

Protein supports fullness by digesting more slowly

Protein also helps with appetite control because it is digested more slowly than many refined carbohydrates. This slower digestion can help you feel satisfied for longer after meals, which may reduce the urge to snack between meals or overeat later in the day. In contrast, highly refined carbohydrate-rich foods are often digested more quickly, which can lead to a faster return of hunger.

Higher thermic effect

Protein has a higher thermic effect of all three macronutrients. The thermic effect of food refers to the energy your body uses to digest, absorb, and metabolise what you eat.

Approximately 20 to 30 percent of protein’s calories are used during digestion and metabolism, compared with around 5 to 10 percent for carbohydrates and 0 to 3 percent for fats. While this does not replace the need for a calorie deficit, it can provide a small metabolic advantage over time. A 2024 systematic review and meta-analysis found that higher-protein meals and diets increased diet-induced thermogenesis and energy expenditure.

Beyond thermogenesis, both the quality and quantity of protein intake influence health and body composition. Adeate protein, particularly from high-quality sources rich in essential amino acids, supports lean mass retention, satiety, and metabolic health. Including a variety of protein sources such as lean meats, fish, eggs, dairy, legumes, and protein supplements, and distributing intake evenly across meals, can further enhance muscle maintenance and appetite control.

How much protein do you actually need?

According to Dietitians Australia protein requirements are typically calculated based on body weight, using grams per kilogram per day (g/kg/day).

For adult women, general protein requirements are around 0.75g per kilogram of body weight per day, while for adult men they are around 0.84g per kilogram per day. People who are pregnant, breastfeeding, or over 70 years of age may require closer to 1g per kilogram per day to support tissue repair, muscle maintenance, and overall health.

It is important to understand that these recommendations represent baseline daily requirements to help prevent deficiency. People who train regularly, want to build or maintain muscle, or are in a fat-loss phase may benefit from higher protein intakes than these minimum targets.

The Bottom Line

Fat loss is not just about eating less, it is about eating strategically.

Protein can help regulate appetite, improve fullness, increase daily energy expenditure through its thermic effect, and support lean muscle mass during a calorie deficit. If you want fat loss to be more sustainable, effective, and supportive of long-term body composition goals, protein should be a core part of your nutrition plan.

Frequently asked questions

Why is protein so important for fat loss?

Protein can help make fat loss more manageable by reducing cravings, increasing satiety, slowing digestion, and increasing the thermic effect of food. This means your body uses more energy to digest protein compared to carbohydrates and fats, while also helping you feel fuller for longer.

How much protein do I need?

Protein needs vary depending on your age, body weight, activity levels, and goals. General daily requirements differ from the higher intakes often used in fat-loss or muscle-maintenance phases. For people focused on fat loss while maintaining muscle, intakes around 1.6 to 2.2 grams per kilogram of body weight per day are often used, although individual needs can vary.

What is the best time to eat protein?

The most important factor is meeting your total daily protein intake consistently. However, spreading protein evenly across meals throughout the day may help support muscle maintenance, recovery, and appetite control more effectively than having most of it in one meal.

REFERENCES

Dietitians Australia. (2023, April 20). Protein. Dietitians Australia. https://dietitiansaustralia.org.au/health-advice/protein

Kohanmoo, A., Faghih, S., & Akhlaghi, M. (2020). Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials. Physiology & Behavior, 226(226), 113123. https://doi.org/10.1016/j.physbeh.2020.113123

Westerterp, K. R. (2004). Diet induced thermogenesis. Nutrition & Metabolism, 1(1), 5. https://doi.org/10.1186/1743-7075-1-5