By long distance walking plus callisthenics, you could burn ~5,000 calories per day. To prevent glycogen breakdown (and consequently ketosis), you would probably need to consume at least 10-15% of calories as carbohydrates, that is *125-190 g carbohydrates per day* ([study 1][1] ; [study 2 - table 2][2]). The amount of digestible carbohydrates (total carb - fiber) and calories in various foods that can be found in wilderness: - [Dandelion][3], 100 g = 5.7 g carbs; 45 kcal - [Blueberries][4], 1,000 g = 121 g carbs; 570 kcal - [Raspberries][5], 1,000 g = 54 g carbs; 520 kcal - [Chestnuts][6], 500 g, roasted = 240 g carbs; 1,225 kcal - [Hazelnuts][7], 200 g = 34 g carbs, 1256 kcal From foods you can find in wilderness, berries and chestnuts are high in carbohydrates, and nuts and animal foods are high in calories. Green vegetables are not high in carbohydrates or calories. In conclusion, to prevent glycogen breakdown during a period of heavy physical activity, you may need to consume more than 100 grams of digestible carbohydrates per day. [1]: https://www.ncbi.nlm.nih.gov/pubmed/29619799 [2]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113752/ [3]: https://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2441/2 [4]: https://nutritiondata.self.com/facts/fruits-and-fruit-juices/1851/2 [5]: https://nutritiondata.self.com/facts/fruits-and-fruit-juices/2053/2 [6]: https://ndb.nal.usda.gov/ndb/foods/show/12167?man=&lfacet=&count=&max=25&qlookup=chestnut&offset=&sort=default&format=Abridged&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&Qv=4&Q328909=1&Q328910=1&Q328911=10.0&Qv=400&Q328909=1&Q328910=1&Q328911=10.0 [7]: https://ndb.nal.usda.gov/ndb/foods/show/12120?man=&lfacet=&count=&max=25&qlookup=hazelnuts&offset=&sort=default&format=Abridged&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&Qv=2&Q328845=1&Q328846=1&Q328847=1&Q328848=1&Q328849=10.0&Qv=1&Q328845=1&Q328846=1&Q328847=1&Q328848=1&Q328849=10.0