Does fasting reduce your ability to eat enough protein?

Intermittent fasting is a popular practice for those who want to lose weight and improve health. While many people enjoy benefits from fasting, some concerns exist — such as whether it’s still possible to eat enough protein to maximize lean mass.

For some, it is indeed challenging to eat 90 to 100 grams of high quality protein in a six-hour window rather than in three meals spread throughout the day. But does that matter?

And, even if you do get enough protein, will consuming it in a narrower window undermine your muscle mass and muscle strength?

A new study suggests it might.

While the study did not examine intermittent fasting, it did examine the evenness of quantities of protein consumed in three time periods: waking to 11:30 am; 11:30 am to 16:30 pm; and 16:30 pm to bedtime. This corresponded roughly to time periods of breakfast, lunch, and dinner.

The researchers followed the food diaries, fitness, and body composition of 192 women, aged 18 to 79. They found that those who ate at least 25 grams or more of protein during each of the three time periods had greater strength and lean mass than those who did not meet the protein target in each of the three time periods. The impact on muscle mass and strength of consuming enough protein across each time period appeared to matter even more in women older than 60. 

Nutrition and Metabolic Insights 2022: Evenness of Dietary Protein Intake Is Positively Associated with Lean Mass and Strength in Healthy Women

This doesn’t prove that you have to eat three meals to get all your protein, but it does suggest that cutting back on meals may put you at a disadvantage for consuming enough protein across enough of the day to maximize your muscle mass and strength.

Our position at Diet Doctor is that intermittent fasting may have health benefits — for the right person. One of the key determinants may be how much protein you can eat during your eating window. (You should target at least 1.6 grams per kilo or 0.7 grams per pound of reference body weight. For more on your individual protein needs, check out our guide with recommended levels.) Another is whether you can sustainably reduce your calories over the day, or if instead you tend to overeat during your eating window. 

When intermittent fasting and eating only two meals each day, some people struggle to reach their daily protein targets of about 50 grams per meal. A protein-rich between-meal snack can help reduce the protein target of your meals, while ensuring you still reach your protein goal. 

Ultimately, if you can’t pack in enough protein into your eating window, we recommend that you prioritize protein over fasting, especially over long time periods.

An important lesson from this study (and others) is that intermittent fasting isn’t a panacea. It’s a tool, like any other, and needs to be used appropriately.

If you are interested in learning more about intermittent fasting, please read our evidence-based guide about fasting for healthy weight loss. 

And you can watch my latest video covering this topic on our YouTube page.

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