Quick answer: Because intermittent fasting shortens your eating window, every meal counts. Focus on nutrient-dense meals with enough protein to protect muscle, plus vitamins, minerals, omega-3s and fiber. Stay well hydrated, and if you snack, choose options rich in protein, fiber and healthy fats rather than refined carbs and sugar.
Key takeaways
Varied whole foods help cover vitamins and minerals, and enough protein in each meal helps maintain muscle.
Staying hydrated matters during fasting, since dehydration can bring dizziness, fatigue, headaches and constipation.
Snacks built on protein, fiber and healthy fats tend to keep energy steadier than refined carbohydrates and sugar.
Eat nutrient-dense meals
Avoid deficiencies with a variety of whole foods, and maintain muscle with enough protein. Support immunity with vitamins A, C, D and E, zinc and selenium, and support the brain with omega-3s, antioxidants and B vitamins. Stay satisfied with protein and fiber.
Stay hydrated
Water supports digestion, circulation, temperature and energy. Dehydration can cause dizziness, fatigue, headaches and constipation. See 16/8 how-to.
Smart snacking
Choose protein, fiber and healthy fats, and avoid refined carbs and sugar that cause energy swings. Plan snacks ahead and eat mindfully.
Snack ideas
- Greek yogurt with berries
- Mixed nuts and seeds
- Hummus with raw vegetables
- Cottage cheese with fruit
- Hard-boiled eggs
- Apple slices with nut butter
- Edamame or roasted chickpeas
- A protein shake or smoothie
Supplements
Some people use a greens drink, MCT oil or protein shake for convenience. See intermittent fasting supplements.
Healthy aging lens
Protein needs rise with age, so make sure each meal in your window includes a quality protein source. See strength training.
What the research shows
Nutrient adequacy during fasting depends on what you eat in your eating window. Trials give some guidance on protein and diet quality.
How much protein supports muscle (Morton 2018, meta-analysis of 49 trials). This review pooled 49 randomized trials with 1,863 healthy adults doing resistance training for at least 6 weeks. Extra protein added about 0.3 kg of lean mass and 2.5 kg to one-rep max strength, and gains leveled off at a total intake of about 1.6 g of protein per kg of body weight a day. A limitation is that these were healthy adults who lifted weights, not people following keto or fasting specifically.
16:8 eating without other changes (Lowe 2020, randomized trial). 116 adults with overweight or obesity either ate only between noon and 8 p.m. or ate three regular meals a day for 12 weeks. The 16:8 group lost an average of 0.94 kg and the regular-meal group 0.68 kg, and the difference between groups (0.26 kg) was not significant. In the in-person subgroup, the 16:8 group lost slightly more lean mass. The main limitation is the short 12-week length, and food intake was self-reported through an app.
Fiber and carbohydrate quality (Reynolds 2019, series of meta-analyses). Commissioned in part by the World Health Organization, this work combined 185 cohort studies and 58 clinical trials with 4,635 trial participants. People with the highest fiber intakes had 15% to 30% lower rates of heart disease, stroke, type 2 diabetes and colorectal cancer than those with the lowest, and the greatest benefit was seen at 25 to 29 g of fiber a day. A limitation is that most of this evidence is observational, and it applies to the general population rather than people with existing chronic disease.
Strength of the evidence: Fasting studies rarely track vitamins and minerals directly, so the evidence here is indirect; focusing on protein and fiber-rich whole foods is a reasonable, well-supported approach.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have diabetes, take blood sugar or blood pressure medication, or have a chronic condition, or if you are pregnant, breastfeeding, underweight, or have a history of disordered eating. The same is true if fasting leaves you dizzy, shaky or exhausted, or if you want a fasting approach tailored to your health goals.
See a medical provider promptly for fainting, confusion, chest pain, a racing heartbeat, or very low blood sugar symptoms such as shaking, sweating and confusion.
Want a fasting plan that fits your health?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
How can I make sure I get enough nutrients and protein within a shorter eating window?
Which foods should I prioritize during my eating window?
How can I make sure I get enough protein and fiber when I eat fewer meals?
Should I adjust what I eat on days I exercise?
Frequently asked questions
How much should I eat when intermittent fasting?
Enough to meet your nutrient and protein needs; fasting isn’t about undereating.
Can I snack during my eating window?
Yes, choose protein- and fiber-rich snacks.
What should I drink while fasting?
Water, herbal tea or black coffee.
Do I need supplements?
Not necessarily; a nutrient-dense diet comes first.
Sources
- Cava E, Yeat NC, Mittendorfer B. Preserving Healthy Muscle during Weight Loss. Adv Nutr 2017. PMID: 28507015. https://pmc.ncbi.nlm.nih.gov/articles/PMC5421125/
- Gombart AF, Pierre A, Maggini S. A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection. Nutrients 2020. PMID: 31963293. https://pmc.ncbi.nlm.nih.gov/articles/PMC7019735/
- Popkin BM, D’Anci KE, Rosenberg IH. Water, hydration, and health. Nutr Rev 2010. PMID: 20646222. https://pmc.ncbi.nlm.nih.gov/articles/PMC2908954/
- Bauer J, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc 2013. PMID: 23867520. https://pubmed.ncbi.nlm.nih.gov/23867520/
- MedlinePlus: Nutrition
- MedlinePlus: Dehydration
- Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 2018. PMID: 28698222. https://pubmed.ncbi.nlm.nih.gov/28698222/
- Lowe DA, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med 2020. PMID: 32986097. https://pubmed.ncbi.nlm.nih.gov/32986097/
- Reynolds A, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet 2019. PMID: 30638909. https://pubmed.ncbi.nlm.nih.gov/30638909/
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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