What Is Intermittent Fasting?

By: dr. Maria Angela, Sp.GK

IIntermittent fasting (IF) is an eating pattern that focuses on when you eat, rather than what you eat. It consists of an "eating window" and a fasting period. During the fasting period, you may only consume water, tea, or black coffee—without any sugar, milk, or creamer.

After several hours of fasting, insulin levels drop, and the body begins to utilize its energy reserves, including fat. However, according to current medical literature, most of the weight loss achieved through intermittent fasting stems primarily from a reduction in total caloric intake, rather than solely from the timing of meals itself.

Types of Intermittent Fasting

The 16:8 method (a form of time-restricted eating, or TRE) is the most popular choice for beginners, as it is relatively easy to incorporate into a daily routine.

• 16:8: Fast for 16 hours, eat within an 8-hour window (e.g., 11:00 AM–7:00 PM). Suitable for beginners.
• 14:10: Fast for 14 hours, eat within a 10-hour window. More flexible and often easier to sustain in the long term.
• 5:2: Eat normally for 5 days, then restrict calorie intake (to approximately 500–600 kcal) on 2 non-consecutive days.
• Alternate-Day Fasting (ADF): Fasting completely or consuming very few calories on alternating days. This requires supervision by a healthcare professional, as there is a higher risk of nutritional deficiency.
• OMAD (One Meal a Day): Meeting all nutritional requirements in a single meal. This is not recommended without strict supervision, as it is difficult to fulfill protein and micronutrient needs.

Benefits of Intermittent Fasting and the Limitations of Scientific Evidence

Some studies suggest that intermittent fasting—specifically time-restricted eating (TRE/16:8)—can help with weight loss and improve certain metabolic markers (such as blood sugar levels, insulin, blood pressure, and lipid profiles) in individuals who are overweight or obese.

However, scientific evidence indicates:

• In the medium to long term, weight loss results are comparable to those of a continuous energy restriction diet.
• Alternate-day fasting may be slightly superior in the short term, but this advantage typically disappears in trials lasting 24 weeks or longer.
• Long-term effects (>1–2 years) and any benefits independent of a caloric deficit remain limited and are not yet fully understood.

Intermittent fasting is an option that may help some people, but it is not a method proven to be universally superior.

Nutritional Needs During Intermittent Fasting

Daily nutritional requirements do not change simply because the eating window is shorter. The principles of a balanced diet must still be followed:

• Include sufficient protein in every meal (eggs, fish, chicken, tofu, tempeh, legumes) to maintain muscle mass.
• Choose complex carbohydrates (brown rice, sweet potatoes, oats, whole-wheat bread).
• Incorporate healthy fats (avocados, nuts, seeds, fatty fish).
• Consume vegetables and fruits as sources of fiber, vitamins, and minerals.
• Ensure adequate fluid intake (plain water) throughout both the fasting and eating periods.
• Maintain an appropriate total calorie intake—overeating within a short window (binge eating) negates the benefits of fasting.

Below is an example of a one-day Intermittent Fasting (IF) menu following the 16:8 pattern:

(Eating window: 11:00 AM–7:00 PM — portion sizes adjusted to individual needs)

• 07:00–10:50: Plain water, tea, or black coffee (unsweetened).
• 11:00 (first meal): Brown rice + grilled fish + stir-fried vegetables + tempeh.
• 15:00 (snack): Unsweetened yogurt + fruit + a handful of nuts.
• 18:30 (last meal): Chicken and vegetable soup + tofu + boiled sweet potato.
• 19:00–07:00: Plain water only.

Who Needs to Be Careful?

Intermittent fasting is not suitable for everyone. Consult with a doctor or nutritionist first if you belong to any of the following groups:

• Pregnant or breastfeeding women
• Children and adolescents who are still in their growth phase
• Individuals with diabetes (especially those using insulin or blood-sugar-lowering medication) — risk of hypoglycemia
• History of eating disorders
• Gastric conditions (gastritis/GERD), kidney disease, heart disease, or liver disorders
• Underweight or malnourished individuals
• Those who regularly take medications that must be consumed with food
• Elderly individuals with underlying medical conditions

Stop immediately and seek medical attention if you experience severe dizziness, fainting, heart palpitations, tremors, or weakness that does not improve.

Common Mistakes Made When Practicing Intermittent Fasting

1. Overeating during the eating window.
2. Neglecting protein and fiber intake.
3. Not drinking enough water.
4. Jumping straight into an extreme regimen (starting with a 12:12 or 14:10 schedule is safer).
5. Failing to adjust exercise routines to the fasting schedule.
6. Pushing yourself even when your body is signaling distress.

Frequently Asked Questions (FAQ)

Is intermittent fasting effective for weight loss?
It can be helpful for some people, primarily because it leads to a reduction in total calorie intake. The results depend heavily on the quality of your diet, portion sizes, physical activity, and consistency. Recent evidence suggests that the outcomes are comparable to those of a standard calorie-restricted diet.

Can I drink coffee or tea while fasting?
Yes, provided they are consumed without sugar, milk, or creamer. Plain water remains the best choice. Individuals with stomach issues should exercise caution when consuming coffee on an empty stomach.

How long should one practice intermittent fasting?
There is no set duration. Evaluate your progress periodically with a healthcare professional. Stop or adjust your approach if you experience any adverse symptoms or if the results do not align with your goals.

Is intermittent fasting the same as fasting during Ramadan?
While both involve restricting the timing of food intake, they are not the same. Fasting during Ramadan also includes the restriction of fluids, whereas intermittent fasting generally allows for the consumption of plain water, tea, and black coffee.

Are vitamin supplements necessary?
Not necessarily. If your diet is balanced and adequate, your nutritional needs can typically be met through food alone. The use of supplements should be based on the assessment of a doctor or a nutritionist.

Conclusion

Intermittent fasting can be a useful dietary approach for weight loss and the improvement of certain metabolic markers, provided that nutritional needs are met and your health status allows for it. A regimen that works for someone else may not necessarily be safe or effective for you. Always consult with a doctor or a nutritionist before starting, especially if you have any underlying medical conditions.

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